10 Questions and Answers About Lithium-Ion Batteries
Lithium-ion batteries are a growing new technology in the industry, especially as the discussion of energy sources continues to be a hot topic worldwide. Existing energy sources (e.g., fossil fuels) are being called for replacement with alternative energy sources (e.g., wind, solar, nuclear) to power the world and economies. Lithium-ion batteries offer the potential for both power and energy storage but also have their own consequences too. Batteries are typically within the electrical engineering realm, but there is always some overlap in the engineering industry, so I would recommend all engineers become familiar with battery technology, regardless of their discipline background.
1. How Do Batteries Store Energy?
Batteries store electricity in a chemical form within a closed system (already you can see the overlap with chemical engineering and thermodynamics!). Some are hopeful that advances in battery technology can solve the energy crisis, and we have already advanced beyond the typical battery use as a power source in small appliances. Devices such as accumulators can store energy for future use, and battery capacity is the quantity of energy storage. Temperature influences battery capacity, with batteries at higher temperatures possessing better capacity than batteries at lower temperatures; however, extremely high temperatures can cause battery damage and undesirable reactivity (e.g., thermal runaway). Lithium-ion batteries have the danger of catching fire and undergoing thermal runaway themselves.
2. What Is Lithium and Why Is It Used in Batteries?
Lithium is the lightest of all metals and has the greatest electrochemical potential, but it can be explosive. In the periodic table (FE Reference Handbook, v 10.0.1, p. 88), lithium is a group 1 alkali metal (e.g., sodium, potassium) and has characteristics of being highly reactive with high energy density. Although lithium itself is unstable (group 1 metals are very reactive), the lithium-ion is more stable (but has a lower energy density). The lithium-ion battery was first introduced in 1991 by the Sony Corporation, and other manufacturers have since sought to commercialize the battery. Graphite and lithium-cobalt oxide are used as electrodes; lithium ions transfer between the anode and cathode. Lithium-ion cells are secondary (rechargeable) cells, so the recharging converts electrical energy back into chemical energy.
3. Why Are Batteries Disposable?
Primary batteries are disposable because the electrochemical reaction cannot be reversed; chemical energy is converted into electrical energy only. Primary cells cannot be recharged; when the cell reaction reaches equilibrium, products migrate away from the electrodes and are consumed by side reactions occurring in the cell. But secondary batteries are rechargeable because the electrochemical reaction can be reversed so voltage can be applied to the battery in the opposite direction of discharge. The electron discharge direction (originally negative to positive) is reversed, restoring power. Rechargeable batteries are often recyclable, including lithium-ion batteries. Oxidized lithium is non-toxic; it can be extracted from a battery and used as feedstock for new lithium-ion batteries.
4. What Is Battery Energy Density?
Lithium-ion batteries offer high energy density and high voltage, along with strong current to power complex mechanical devices. Battery energy density is the amount of energy a battery contains for its given weight and size. These batteries also have good longevity; their shelf-life is only 5% discharge per month. The longevity is an important factor since lithium-ion batteries do not lose their features rapidly. They can be stored and transported for long periods and still maintain their qualities. Battery weight and size is generally a limiting factor for developing electronic devices; you have probably seen it in everyday life with television remotes and other handhelds. Many of these device designs are dictated by the battery design since the battery is their power source after all.
5. How Can We Improve Batteries?
Lithium-ion batteries are also compatible with nanoscale materials, creating more possibilities for their potential (did you like the pun?). Electrodes can be optimized by designing their structures on the nanoscale level. With nanoscale technology, objects can be manufactured at the atomic and molecular level. And since nanoparticles have little volume expansion, this improves the rechargeable reversibility of lithium-ion batteries. Lithium diffusion rates are slow, so the battery can continue the reversibility cycle without losing much charge. Carbon nanotubes can serve as a potential electrode for lithium-ion batteries. Carbon can be anodic with its unique structural and mechanical properties. Remember that oxidation occurs at the anode, and reduction happens at the cathode. The anode is the positive side where the electricity moves into by attracting electrons.
6. What Are Some Commercial Applications of Batteries?
Nanotech and lithium-ion batteries can be commercialized; this combination can provide lighter, more powerful batteries that can increase user mobility and equipment life. This is the best of both worlds since you have the very small nanoscale but with high energy density. Another commercial application is that lithium-ion batteries can coexist with other renewable technologies. Because they are light, can recharge quickly, and hold charge for a long while, they have the design flexibility to be used with wind and solar generators. The lightness and power volume enable storage flexibility too.
7. What Are Some Disadvantages of Batteries?
While lithium-ion batteries can be an advantageous technology, they do have their disadvantages. Lithium-ion batteries are expensive, and the battery temperatures are delicate, so they are subject to regulations. Vibration, shock, and forced discharge can all cause undesirable battery defects, so lithium-ion batteries must follow shipment and transportation regulations. Lithium-ion batteries contain corrosive and flammable electrolytes and are considered a hazardous material by the United States Department of Transportation (USDOT). According to Environmental Protection Agency (EPA) standards, lithium-ion batteries must be disposed in separate recycling and waste collection points.
8. How Can You Safely Store Batteries?
The batteries also require high capacity and high operating voltage to function properly. Storage installations in the United States have demonstrated concerns over battery safety. In April 2019, the McMicken event was one such example. Arizona Public Service (APS) is the largest electric utility in Arizona, and the company had invested heavily in batteries for energy storage projects. A grid battery fire occurred near Phoenix due to a lithium-ion battery defect; this led to an explosion that triggered a chain reaction, releasing explosive gases. While lithium-ion batteries possess good longevity, the batteries can still degrade over time, losing their shelf life. Degradation can cause a short circuit, heating up the batteries, and triggering thermal runaway.
9. What Is Thermal Runaway?
Thermal runaway is a form of uncontrollable combustion, releasing heat as an exothermic reaction. First responders were injured due to the reaction, but fortunately, the storage facility was relatively remote, so the battery accident did not result in a catastrophic loss of human life. Still, this incident delayed future battery projects for APS and discouraged confidence in pursuing lithium-ion battery technology. The primary disadvantage with lithium-ion batteries is safety concerns and rightfully so, as safety should always be first priority in the engineering industry. Thermal runaway can rapidly increase its severity causing devastating fires and explosions. Heat released speeds up the reaction which causes more heat release that can eventually lead to scorched earth, property damage, and fatalities.
10. What Happens When You Link Battery Cells?
Linking battery cells increases system energy capacity but also increases failure probability. Heat dissipation is also more difficult on larger-scale systems. There are few simulation tools that can accurately predict the probability of battery failure or degradation; testing must be conducted to achieve reasonable estimates. For lithium-ion batteries to become a mainstay of commercial energy storage, there must be improved guaranteed safety measures designed into large-scale systems. This is the trade-off; battery chemistry can produce high energy storage, but the same chemistry produces high reactivity. The key challenge is designing battery systems that can maximize energy storage but minimize reactivity; if this were achievable, you would have a truly superior battery.
Lithium battery technology is an exciting and growing field; there are many new challenges and opportunities ahead. Oftentimes more research and learning will lead to more questions that require further research for resolutions. For example, lithium-air batteries have recently been investigated by scientists and supposedly have a very high energy density, even greater than lithium-ion batteries. Be sure to check with School of PE for more technological and industry news, as there may be a succeeding blog post about lithium-air batteries!
Are you feeling "charged" about batteries and their importance in our daily lives? Engineers are integral in innovating and improving battery technology-if you are interested in becoming a professional engineer, a partnership with School of PE is just what you need to get started on the right track. Our subject-matter expert instructors and comprehensive materials will help you succeed on exam day! Register now for a course.