AIM

To understand different battery chemistry.

INTRODUCTION

1.       ELECTRIC SCOOTER/VEHICLE:

[1] Electric motorcycles and scooters are plug-in electric vehicles with two or three wheels. The electricity is stored on board in a rechargeable battery, which drives one or more electric motors. Electric scooters (as distinct from motorcycles) have a step-through frame. Most electric motorcycles and scooters as of May 2019 are powered by rechargeable lithium-ion batteries, though some early models used nickel-metal hydride batteries. Alternative types of batteries are available. Z Electric Vehicle has pioneered use of a lead/sodium silicate battery (a variation on the classic lead acid battery invented in 1859, still prevalent in automobiles) that compares favorably with lithium batteries in size, weight, and energy capacity, at considerably less cost. E-Gen says its lithium-iron phosphate batteries are up to two-thirds lighter than lead acid batteries and offer the best battery performance for electric vehicles. In 2017, the first vehicle in the US to use the new Lithium Titanium Oxide (LTO) battery non-flammable battery technology is a scooter called The Expresso. This new technology charges a battery in less than 10 minutes and withstands 25,000 charges (the equivalent of 70 years of daily charges). The technology, created by Altair-nano, is currently being used in China where over 10,000 urban buses run on these fast charge batteries.

2.     BATTERY:

A battery is a power source consisting of one or more electrochemical cells with external connections for powering electrical devices such as flashlights, mobile phones, and electric cars. When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode. The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal. When a battery is connected to an external electric load, a redox reaction converts high-energy reactants to lower-energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Historically the term "battery" specifically referred to a device composed of multiple cells, however the usage has evolved to include devices composed of a single cell. Primary (single-use or "disposable") batteries are used once and discarded, as the electrode materials are irreversibly changed during discharge; a common example is the alkaline battery used for flashlights and a multitude of portable electronic devices. Secondary (rechargeable) batteries can be discharged and recharged multiple times using an applied electric current; the original composition of the electrodes can be restored by reverse current. Examples include the lead-acid batteries used in vehicles and lithium-ion batteries used for portable electronics such as laptops and mobile phones.

Figure 1. Various cells and batteries (top left to bottom right): two AA, one D, one handheld ham radio battery, two 9-volt (PP3), two AAA, one C, one camcorder battery, one cordless phone battery.

Batteries come in many shapes and sizes, from miniature cells used to power hearing aids and wristwatches to small, thin cells used in smartphones, to large lead acid batteries or lithium-ion batteries in vehicles, and at the largest extreme, huge battery banks the size of rooms that provide standby or emergency power for telephone exchanges and computer data centers. Batteries have much lower specific energy (energy per unit mass) than common fuels such as gasoline. In automobiles, this is somewhat offset by the higher efficiency of electric motors in converting electrical energy to mechanical work, compared to combustion engines.

3.      LITHIUM-ION BATTERY:

[3] A lithium-ion (Li-ion) battery is an advanced battery technology that uses lithium ions as a key component of its electrochemistry. During a discharge cycle, lithium atoms in the anode are ionized and separated from their electrons. The lithium ions move from the anode and pass through the electrolyte until they reach the cathode, where they recombine with their electrons and electrically neutralize. The lithium ions are small enough to be able to move through a micro-permeable separator between the anode and cathode. In part because of lithium’s small size (third only to hydrogen and helium), Li-ion batteries are capable of having a very high voltage and charge storage per unit mass and unit volume.

Li-ion batteries can use a number of different materials as electrodes. The most common combination is that of lithium cobalt oxide (cathode) and graphite (anode), which is most commonly found in portable electronic devices such as cellphones and laptops. Other cathode materials include lithium manganese oxide (used in hybrid electric and electric automobiles) and lithium iron phosphate. Li-ion batteries typically use ether (a class of organic compounds) as an electrolyte.

[4] Li-ion is a low-maintenance battery, an advantage that most other chemistries cannot claim. The battery has no memory and does not need exercising (deliberate full discharge) to keep it in good shape. Self-discharge is less than half that of nickel-based systems and this helps the fuel gauge applications. The nominal cell voltage of 3.60V can directly power mobile phones, tablets, and digital cameras, offering simplifications and cost reductions over multi-cell designs. The drawbacks are the need for protection circuits to prevent abuse, as well as high price.

Lithium-ion uses a cathode (positive electrode), an anode (negative electrode) and electrolyte as conductor. (The anode of a discharging battery is negative and the cathode positive. The cathode is metal oxide, and the anode consists of porous carbon. During discharge, the ions flow from the anode to the cathode through the electrolyte and separator; charge reverses the direction and the ions flow from the cathode to the anode. Figure 2 illustrates the process.

Figure 2. Discharging and Charging of the Lithium-Ion battery.

When the cell charges and discharges, ions shuttle between cathode (positive electrode) and anode (negative electrode). On discharge, the anode undergoes oxidation, or loss of electrons, and the cathode sees a reduction, or a gain of electrons. Charge reverses the movement.

Sony’s original lithium-ion battery used coke as the anode (coal product). Since 1997, most Li ion manufacturers, including Sony, shifted to graphite to attain a flatter discharge curve. Graphite is a form of carbon that has long-term cycle stability and is used in lead pencils. It is the most common carbon material, followed by hard and soft carbons. Nanotube carbons have not yet found commercial use in Li-ion as they tend to entangle and affect performance. A future material that promises to enhance the performance of Li-ion is graphene.

Figure 3. Voltage discharge curve of Lithium-Ion.

A battery should have a flat voltage curve in the usable discharge range. The modern graphite anode does this better than the early coke version. Several additives have been tried, including silicon-based alloys, to enhance the performance of the graphite anode. It takes six carbon (graphite) atoms to bind to a single lithium ion; a single silicon atom can bind to four lithium ions. This means that the silicon anode could theoretically store over 10 times the energy of graphite, but expansion of the anode during charge is a problem. Pure silicone anodes are therefore not practical and only 3–5 percent of silicon is typically added to the anode of a silicon-based to achieve good cycle life.

Using nano-structured lithium-titanate as an anode additive shows promising cycle life, good load capabilities, excellent low-temperature performance, and superior safety, but the specific energy is low, and the cost is high. Experimenting with cathode and anode material allows manufacturers to strengthen intrinsic qualities, but one enhancement may compromise another. The so-called “Energy Cell” optimizes the specific energy (capacity) to achieve long runtimes but at lower specific power; the “Power Cell” offers exceptional specific power but at lower capacity. The “Hybrid Cell” is a compromise and offers a little bit of both.

 Manufacturers can attain a high specific energy and low cost relatively easily by adding nickel in lieu of the more expensive cobalt, but this makes the cell less stable. While a start-up company may focus on high specific energy and low price to gain quick market acceptance, safety and durability cannot be compromised. Reputable manufacturers place high integrity on safety and longevity. Most Li-ion batteries share a similar design consisting of a metal oxide positive electrode (cathode) that is coated onto an aluminum current collector, a negative electrode (anode) made from carbon/graphite coated on a copper current collector, a separator and electrolyte made of lithium salt in an organic solvent. Table 1 summarizes the advantages and limitations of Li-ion.

 Table 1. Advantages and Limitations of Lithium-Ion battery.

OBJECTIVES

• To calculate the maximum speed of the motor used in an electric scooter with defined parameters.
• To prepare a simple excel calculator to identify vehicle propulsion power based on given inputs and outputs.
• Understanding the effect of pressure difference on rolling resistance and total traction power.
• Understanding the forces acting on the Range Rover under given conditions.

PROBLEM SPECIFICATION AND SOLVING:

PROBLEM STATEMENT I:

Prepare a table which includes materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP and LTO type of lithium-ion cells. Give your detailed explanation on it.

EXPLANATION AND OBSERVATION:

1. LITHIUM COBALT OXIDE (LCO): [5] The chemical formula is LiCoO₂.Its high specific energy makes Li-cobalt the popular choice for mobile phones, laptops, and digital cameras. The battery consists of a cobalt oxide cathode and a graphite carbon anode. The cathode has a layered structure and during discharge, lithium ions move from the anode to the cathode. The flow reverses on charge. The drawback of Li-cobalt is a relatively short life span, low thermal stability, and limited load capabilities (specific power).

Figure 4. Li-Cobalt structure.

The cathode has a layered structure. During discharge the lithium ions move from the anode to the cathode; on charge the flow is from cathode to anode. The drawback of Li-cobalt is a relatively short life span, low thermal stability, and limited load capabilities (specific power). Like other cobalt-blended Li-ion, Li-cobalt has a graphite anode that limits the cycle life by a changing solid electrolyte interface (SEI), thickening on the anode and lithium plating while fast charging and charging at low temperature. Newer systems include nickel, manganese and/or aluminum to improve longevity, loading capabilities and cost.

Li-cobalt should not be charged and discharged at a current higher than its C-rating. This means that an 18650 cell with 2,400mAh can only be charged and discharged at 2,400mA. Forcing a fast charge or applying a load higher than 2,400mA causes overheating and undue stress. For optimal fast charge, the manufacturer recommends a C-rate of 0.8C or about 2,000mA. (See BU-402: What is C-rate).

Figure 5. Lithium Cobalt Oxide battery working during Discharge.

The mandatory battery protection circuit limits the charge and discharge rate to a safe level of about 1C for the Energy Cell. The hexagonal spider graphic (Figure 6) summarizes the performance of Li-cobalt in terms of specific energy or capacity that relates to runtime; specific power or the ability to deliver high current; safety; performance at hot and cold temperatures; life span reflecting cycle life and longevity; and cost. Other characteristics of interest not shown in the spider webs are toxicity, fast-charge capabilities, self-discharge and shelf life. (See BU-104c: The Octagon Battery – What makes a Battery a Battery).

Figure 6. Snapshot of an average Li-cobalt battery.

The Li-cobalt is losing favor to Li-manganese, but especially NMC and NCA because of the high cost of cobalt and improved performance by blending with other active cathode materials. The anodic, cathodic and the overall reactions for Lithium Cobalt oxide are as follows:

Table 2. Characteristics of Lithium Cobalt Oxide.

2. LITHIUM MANGANESE OXIDE (LMO): [5] In 1996, Moli Energy commercialized a Li-ion cell with lithium manganese oxide as cathode material. The architecture forms a three-dimensional spinel structure that improves ion flow on the electrode, which results in lower internal resistance and improved current handling. A further advantage of spinel is high thermal stability and enhanced safety, but the cycle and calendar life are limited. Low internal cell resistance enables fast charging and high-current discharging. In an 18650 package, Li-manganese can be discharged at currents of 20–30A with moderate heat buildup. It is also possible to apply one-second load pulses of up to 50A. A continuous high load at this current would cause heat buildup and the cell temperature cannot exceed 80°C (176°F). Li-manganese is used for power tools, medical instruments, as well as hybrid and electric vehicles.

Figure 7. Li-Manganese structure.

Figure 7 illustrates the formation of a three-dimensional crystalline framework on the cathode of a Li-manganese battery. This spinel structure, which is usually composed of diamond shapes connected into a lattice, appears after initial formation. The cathode crystalline formation of lithium manganese oxide has a three-dimensional framework structure that appears after initial formation. Spinel provides low resistance but has a more moderate specific energy than cobalt. Li-manganese has a capacity that is roughly one-third lower than Li-cobalt. Design flexibility allows engineers to maximize the battery for either optimal longevity (life span), maximum load current (specific power) or high capacity (specific energy). For example, the long-life version in the 18650 cell has a moderate capacity of only 1,100mAh; the high-capacity version is 1,500mAh. Figure 8 shows the spider web of a typical Li-manganese battery. The characteristics appear marginal but newer designs have improved in terms of specific power, safety, and life span. Pure Li-manganese batteries are no longer common today; they may only be used for special applications.

Figure 8. Snapshot of an average Li-Manganese battery.

Although moderate in overall performance, newer designs of Li-manganese offer improvements in specific power, safety and life span. Most Li-manganese batteries blend with lithium nickel manganese cobalt oxide (NMC) to improve the specific energy and prolong the life span. This combination brings out the best in each system, and the LMO (NMC) is chosen for most electric vehicles, such as the Nissan Leaf, Chevy Volt and BMW i3. The LMO part of the battery, which can be about 30 percent, provides high current boost on acceleration; the NMC part gives the long driving range.

Figure 9. Lithium Manganese Oxide battery layout.

Table 3. Characteristics of Lithium Manganese Oxide.

Li-ion research gravitates heavily towards combining Li-manganese with cobalt, nickel, manganese and/or aluminum as active cathode material. In some architecture, a small amount of silicon is added to the anode. This provides a 25 percent capacity boost; however, the gain is commonly connected with a shorter cycle life as silicon grows and shrinks with charge and discharge, causing mechanical stress. These three active metals, as well as the silicon enhancement can conveniently be chosen to enhance the specific energy (capacity), specific power (load capability) or longevity. While consumer batteries go for high capacity, industrial applications require battery systems that have good loading capabilities, deliver a long life and provide safe and dependable service.

The anodic, cathodic and the overall reactions for Lithium Manganese oxide are as follows:

3. LITHIUM NICKEL COBALT ALUMINIUM OXIDE (NCA): [5] Lithium nickel cobalt aluminum oxide battery, or NCA, has been around since 1999 for special applications. It shares similarities with NMC by offering high specific energy, reasonably good specific power, and a long-life span. Less flattering are safety and cost.

Figure 10. Components of Lithium Nickel Cobalt Aluminium Oxide battery layout.

[6] The lithium nickel cobalt aluminium oxides (NCA) are a group of substances comprising metal oxides. Some of them are important due to their application in lithium-ion batteries. NCAs are used as active material on the positive pole. NCAs are mixed oxides comprising the cations of the chemical elements lithium, nickel, cobalt, and aluminium. The most important representatives have the general formula LiNixCoyAlzO2 with x + y + z = 1. In case of the NCA comprising batteries currently available on the market, which are also used in electric cars and electric appliances, x ≈ 0,8, and the voltage of those batteries is between 3.6 V and 4.0 V, at a nominal voltage of 3.6 V or 3.7 V. A version of the oxides currently in use in 2019 is LiNi0,84Co0,12Al0,04O2.

[5] Figure 11 summarizes the six key characteristics. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability. High energy and power densities, as well as good life span, make NCA a candidate for EV powertrains. High cost and marginal safety are negatives.

Figure 11. Snapshot of an average Li-Nickel Cobalt Aluminium oxide battery.

[6] The most important manufacturer of NCA batteries is Panasonic or Panasonic's cooperation partner Tesla, as Tesla uses NCA as active material in the traction batteries of its car models. In Tesla Model 3 and Tesla Model X, LiNi0,84Co0,12Al0,04O2 is used.

With a few exceptions, current electric cars as of 2019 use either NCA or alternatively lithium nickel manganese cobalt oxides (NMC). In addition to use in electric cars, NCA is also used in batteries for electronic devices, mainly by Panasonic, Sony, and Samsung. Cordless vacuum cleaners are also equipped with NCA batteries.

The anodic, cathodic and the overall reactions for Lithium Nickel Cobalt Aluminium oxide are as follows:

Table 4. Characteristics of Lithium Nickel Cobalt Aluminium Oxide.

4. LITHIUM NICKEL MANGANESE COBALT OXIDE (NMC): [4] One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be tailored to serve as Energy Cells or Power Cells. For example, NMC in an 18650 cell for moderate load condition has a capacity of about 2,800mAh and can deliver 4A to 5A; NMC in the same cell optimized for specific power has a capacity of only about 2,000mAh but delivers a continuous discharge current of 20A. A silicon-based anode will go to 4,000mAh and higher but at reduced loading capability and shorter cycle life. Silicon added to graphite has the drawback that the anode grows and shrinks with charge and discharge, making the cell mechanically unstable. The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt in which the main ingredients, sodium, and chloride, are toxic on their own but mixing them serves as seasoning salt and food preserver.

Figure 12. Variations of Lithium Nickel Manganese Cobalt Oxide battery composition.

Nickel is known for its high specific energy but poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers a low specific energy. Combining the metals enhances each other strengths. NMC is the battery of choice for power tools, e-bikes, and other electric powertrains. The cathode combination is typically one-third nickel, one-third manganese, and one-third cobalt, also known as 1-1-1. Cobalt is expensive and in limited supply. Battery manufacturers are reducing the cobalt content with some compromise in performance. A successful combination is NCM532 with 5 parts nickel, 3 parts cobalt and 2 parts manganese. Other combinations are NMC622 and NMC811. Cobalt stabilizes nickel, a high energy active material. New electrolytes and additives enable charging to 4.4V/cell and higher to boost capacity. Figure 13 demonstrates the characteristics of the NMC.

Figure 13. Snapshot of an average Li-Nickel Manganese Cobalt oxide battery.

NMC has good overall performance and excels on specific energy. This battery is the preferred candidate for the electric vehicle and has the lowest self-heating rate. There is a move towards NMC-blended Li-ion as the system can be built economically and it achieves a good performance. The three active materials of nickel, manganese and cobalt can easily be blended to suit a wide range of applications for automotive and energy storage systems (ESS) that need frequent cycling. The NMC family is growing in its diversity. The cathodic, anodic and the overall reactions for Lithium Nickel Manganese Cobalt oxide are as follows:

Table 5. Characteristics of Lithium Nickel Manganese Cobalt Oxide.

5. LITHIUM IRON PHOSPHATE (LPF): [4] In 1996, the University of Texas (and other contributors) discovered phosphate as cathode material for rechargeable lithium batteries. Li-phosphate offers good electrochemical performance with low resistance. This is made possible with nano-scale phosphate cathode material. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety, and tolerance if abused. Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time. As a trade-off, its lower nominal voltage of 3.2V/cell reduces the specific energy below that of cobalt-blended lithium-ion. With most batteries, cold temperature reduces performance and elevated storage temperature shortens the service life, and Li-phosphate is no exception. Li-phosphate has a higher self-discharge than other Li-ion batteries, which can cause balancing issues with aging. This can be mitigated by buying high quality cells and/or using sophisticated control electronics, both of which increase the cost of the pack. Cleanliness in manufacturing is of importance for longevity. There is no tolerance for moisture, lest the battery will only deliver 50 cycles

Figure 14. Composition of Lithium Iron Phosphate battery.

Li-phosphate is often used to replace the lead acid starter battery. Four cells in series produce 12.80V, a similar voltage to six 2V lead acid cells in series. Vehicles charge lead acid to 14.40V (2.40V/cell) and maintain a topping charge. Topping charge is applied to maintain full charge level and prevent sulfation on lead acid batteries. With four Li-phosphate cells in series, each cell tops at 3.60V, which is the correct full-charge voltage. At this point, the charge should be disconnected but the topping charge continues while driving. Li-phosphate is tolerant to some overcharge; however, keeping the voltage at 14.40V for a prolonged time, as most vehicles do on a long road trip, could stress Li-phosphate. Time will tell how durable Li-Phosphate will be as a lead acid replacement with a regular vehicle charging system. Cold temperature also reduces performance of Li-ion and this could affect the cranking ability in extreme cases. Figure 15 summarizes the attributes of Li-phosphate. Li-phosphate has excellent safety and long-life span but moderate specific energy and elevated self-discharge. The anodic, cathodic and the overall reactions for Lithium Iron Phosphate are as follows:

Figure 15. Snapshot of an average Lithium Iron Phosphate battery.

Table 6. Characteristics of Lithium Iron Phosphate.

6. LITHIUM TITANATE (LTO): [4] Batteries with lithium titanate anodes have been known since the 1980s. Li-titanate replaces the graphite in the anode of a typical lithium-ion battery and the material forms into a spinel structure. The cathode can be lithium manganese oxide or NMC. Li-titanate has a nominal cell voltage of 2.40V, can be fast charged and delivers a high discharge current of 10C, or 10 times the rated capacity. The cycle count is said to be higher than that of a regular Li-ion. Li-titanate is safe, has excellent low-temperature discharge characteristics and obtains a capacity of 80 percent at –30°C (–22°F).

Figure 16. Construction and Operating Principle of Lithium Titanate battery.

LTO (commonly Li₄Ti₅O₁₂) has advantages over the conventional cobalt-blended Li-ion with graphite anode by attaining zero-strain property, no SEI film formation and no lithium plating when fast charging and charging at low temperature. Thermal stability under high temperature is also better than other Li-ion systems; however, the battery is expensive. At only 65Wh/kg, the specific energy is low, rivalling that of NiCd. Li-titanate charges to 2.80V/cell, and the end of discharge is 1.80V/cell. Figure 17 illustrates the characteristics of the Li-titanate battery. Typical uses are electric powertrains, UPS, and solar-powered street lighting.

Figure 17. Snapshot of an average Lithium Titanate battery.

Li-titanate excels in safety, low-temperature performance, and life span. Efforts are being made to improve the specific energy and lower cost. The anodic, cathodic and the overall reactions for Lithium Titanate (Li₂TiO₃)  are as follows:

The anodic, cathodic and the overall reactions for Lithium Titanate (Li₄Ti₅O₁₂) are as follows:

Table 7. Characteristics of Lithium Titanate.

PROBLEM STATEMENT II:

Compare the differences between each type of Li⁺ ion batteries based on their characteristics

EXPLANATION AND OBSERVATION:

• The difference between the battery in the basic chemical construction is as follows:

Table 8. Basic chemical compositions of different Lithium-Ion Batteries. [*In organic solvents such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate]

• The difference between different Lithium-Ion batteries with respect to electrical aspects is tabulated as follows:

Table 9. Comparison of electrical aspects of different types of Lithium-Ion batteries. [*related to depth of discharge, load, temperature]

• The difference between different Lithium-Ion batteries in thermal aspect is tabulated as follows:

Table 9. Comparison of Thermal aspects of different types of Lithium-Ion batteries.

Thermal runaway : Lithium-ion (Li-ion) battery thermal runaway occurs when a cell, or area within the cell, achieves elevated temperatures due to thermal failure, mechanical failure, internal/external short circuiting, and electrochemical abuse. At elevated temperatures, exothermic decomposition of the cell materials begins. Eventually, the self-heating rate of the cell is greater than the rate at which heat can be dissipated to the surroundings, the cell temperature rises exponentially, and stability is ultimately lost. The loss in stability results in all remaining thermal and electrochemical energy being released to the surroundings. [7]

• The various applications of different types of Lithium-Ion batteries is as follows:

Table 10. Comparison of applications of different types of Lithium-Ion batteries.

RESULTS

• The list of the anodic, cathodic, and overall reactions in different Lithium-Ion batteries is as follows:

Table 11. Comparison of anodic, cathodic, and overall reactions of different types of Lithium-Ion batteries.

• On comparison of different types of Lithium-ion batteries and the rest, we have:

While Li-aluminum (NCA) is the clear winner by storing more capacity than other systems, this only applies to specific energy. In terms of specific power and thermal stability, Li-manganese (LMO) and Li-phosphate (LFP) are superior. Li-titanate (LTO) may have low capacity but this chemistry outlives most other batteries in terms of life span and also has the best cold temperature performance. Moving towards the electric powertrain, safety and cycle life will gain dominance over capacity. (LCO stands for Li-cobalt, the original Li-ion.)

Figure 18. Typical specific energy of lead-, nickel- and lithium-based batteries.

NCA enjoys the highest specific energy; however, manganese and phosphate are superior in terms of specific power and thermal stability. Li-titanate has the best life span. The figure 19 shows the variation of different features of Lithium Ion batteries.

Figure 19. Representation of different types of parameters of different Lithium-Ion batteries.

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BIBLIOGRAPHY

1. https://en.wikipedia.org/wiki/Electric_motorcycles_and_scooters
2. https://en.wikipedia.org/wiki/Electric_battery
3. https://www.cei.washington.edu/education/science-of-solar/battery-technology/
4. https://batteryuniversity.com/index.php/learn/article/lithium_based_batteries
5. https://batteryuniversity.com/learn/article/types_of_lithium_ion
6. https://en.wikipedia.org/wiki/Lithium_nickel_cobalt_aluminium_oxides
7. https://www.batterypoweronline.com/news/thermal-runaway-understanding-the-fundamentals-to-ensure-safer-batteries/