Lithium-ion (Li-ion) batteries have helped power society’s shift to renewable energy, serving as the industry standard for everything from electric vehicles to grid-scale energy storage. Because Li-ion batteries come with safety risks and environmental consequences in their production, scientists are continually looking for sustainable alternatives to lithium batteries. Here is a look at the history and challenges of Li-ion and how emerging technologies strive to replace the batteries while balancing performance, cost, and environmental impact.
What Is a Lithium-Ion Battery?
- A lithium-ion battery consists of four main components:
• a cathode, the positive electrode
• an anode, which is the negative electrode
• an electrolyte, the medium for lithium-ion movement
• a separator, the permeable barrier between the electrodes
- The cathodes of Li-ion batteries may be any of the following:
• lithium nickel manganese cobalt oxide (NMC)
• lithium nickel cobalt aluminum oxide (NCA)
• lithium cobalt oxide (LCO)
• lithium iron phosphate (LFP / LiFePO4)
• lithium manganese oxide (LMO)
• lithium titanate oxide (LTO)
• other lithium-based compounds
The anode of a Li-ion battery is primarily composed of carbon, usually graphite, though other materials like lithium titanium oxide and silicon are also used in some. The electrolyte is typically a lithium salt (LiPF6) dissolved in an organic solvent.
Lithium ions move from the anode to the cathode during the discharge (or usage) process, creating a flow of electrons to power devices. When the battery is charging, the process is reversed, with lithium ions moving back to the anode.
The History of Lithium-Ion Batteries
The history of lithium-ion battery technology dates back to the 1970s when researchers began exploring the potential of lithium as a battery material due to its low electrochemical potential. In the 1980s, Sony introduced the first commercial lithium-ion batteries using lithium cobalt oxide as the cathode material.
Over the years, scientists have developed different cathode materials like lithium iron phosphate (LFP / LiFePO4) and lithium nickel manganese cobalt oxide (NMC) to improve the safety, stability, and energy density of Li-ion batteries. Researchers continue to explore new materials and technologies to enhance the performance of battery technology, aiming to increase energy storage capacity and reduce costs.
Negative Effects of Lithium-Ion Batteries
Even though they are promoted as a way to mitigate climate change, lithium-ion batteries cause damage to the environment during their manufacturing. For instance, every ton of lithium extracted through hard-rock mining results in 15 metric tons of carbon dioxide emissions. Moreover, the technology uses a narrow set of raw materials — lithium, cobalt, and nickel, among others — controlled by a handful of countries in South America, Asia, and Africa.
This far-flung supply chain not only leads to high transportation costs but also results in a number of environmental and ethical issues:
• Lithium mining has been associated with accelerating drought and displacing Indigenous populations in countries ranging from Chile to Serbia.
• Most of the world’s lithium refining facilities are in China, which is notorious for its abundant use of heavily polluting coal.
• Cobalt mining in the Democratic Republic of Congo is known for exploiting child labor, displacing residents, and damaging the environment.
• Nickel mining in Indonesia has contributed to deforestation, soil erosion, and water pollution.
Lithium-ion batteries also pose significant safety risks. Their organic electrolytes are flammable at temperatures as low as 60 degrees Celsius, and improper use can cause them to overheat. Before a battery cell in thermal runaway actually catches flame, it vents flammable gases such as hydrogen fluoride and carbon monoxide. These toxic vapors can cause an explosion when they ignite, making Li-ion battery fires especially dangerous, even “safer” chemistries like LFP / LiFePO4.
Alternatives to Lithium-Ion Batteries
Some companies are looking into lithium-sulfur (Li-S) batteries as a sustainable alternative to Li-ion. Rather than relying on scarce materials like cobalt, Li-S batteries would benefit from the wider availability of sulfur, making them less dependent on limited resources and cheaper to produce. Li-S batteries also have a theoretical energy density several times higher than that of lithium-ion batteries, storing an equal amount of energy in a more lightweight form.
However, Li-S batteries tend to degrade more rapidly due to poor cycling stability. Sulfur does not have high electrical conductivity to begin with. It also undergoes significant volume expansion and contraction during charge and discharge, resulting in the dissolution of active material and a loss of charge capacity. Additionally, the chemical reaction between sulfur and lithium results in the formation of compounds that reduce Li-S batteries’ efficiency over time.
Further, in Li-S batteries, lithium metal supplants the graphite anode. Li metal anodes have a host of other issues associated with dendritic plating, excessive Li consumption in the formation of SEI, and an increased risk of thermal runaway from shorting.
Solid-State Lithium Batteries
Instead of a flammable liquid electrolyte, solid-state lithium batteries use a solid electrolyte to reduce the risk of fires caused by thermal runaway. Solid-state batteries can potentially pack more energy into a smaller space, making them useful for applications like EVs where more energy translates to more miles per charge.
Solid-state batteries may also exhibit better cycling stability, which is the ability of a battery to maintain its performance and capacity over repeated discharge cycles without significant degradation. Additionally, they can potentially operate over a wider temperature range, making them more suitable for extreme environments.
Despite recent advancements in solid-state technology, scientists are still trying to find an electrolyte that simultaneously offers high conductivity, stability, and low manufacturing costs. The most promising solid-state battery chemistries have been difficult to scale up for mass production at an affordable price point, and developers need a cost-effective means of manufacturing the batteries before they can be used commercially.
And while solid-state batteries may be safer when it comes to thermal runaway imposed by normal operation, researchers at Sandia National Labs have concluded that they could pose similar risks as traditional lithium-ion batteries when punctured or crushed.
Sodium-ion batteries are a type of rechargeable battery that operate in a similar way to lithium-ion batteries, but use sodium ions (Na+) instead of lithium ions (Li+). The cathode is often made of materials like sodium cobaltate or copper hexacyanoferrate. The anode can be made of materials like hard carbon, soft carbon, or titanium-based compounds.
Sodium-ion batteries are considered a potential solution to the scarcity and cost associated with lithium resources. The technology can be manufactured using existing infrastructure and equipment designed for Li-ion batteries, making it easier to scale up production and integrate sodium-ion batteries into existing energy storage systems. They are also reported to have a lower risk of thermal runaway and a lower environmental impact in the manufacturing process.
Unfortunately, sodium-ion batteries generally have lower energy density than Li-ion batteries and currently have trouble maintaining stable performance over repeated charge and discharge cycles. They typically have longer charging times compared to Li-ion batteries, which can limit their suitability for applications that require fast charging. And because the technology is still in the early stages of commercialization, it will be a while before they are widely available. Sodium metal, like lithium metal, is also highly reactive and flammable and Na-ion batteries also require a flammable organic electrolyte. Though Na-ion cells may be less energetic than Li-ion, they still pose a significant safety risk.
Iron-air batteries are a type of metal-air battery that use iron as the anode and atmospheric oxygen reactions with a catalyst as the cathode, coupled with an electrolyte to facilitate the charge transfer. First studied in the 1970s, the operating theory is that during discharge, the metallic iron anode oxidizes to iron oxide by reacting with hydroxyl ions in the electrolyte. At the same time, oxygen from the air is reduced at the cathode, forming hydroxyl ions. These reactions produce water and an electric current. During charge, iron oxide at the anode is reduced to metallic iron, and hydroxide ions from the electrolyte react with a catalyst at the cathode to generate oxygen and water.
Iron-air batteries use abundant and non-toxic raw materials, and have a very high theoretical energy density (potentially higher than lithium-ion batteries). However, iron-air batteries also have several challenges to overcome. First, they have low Coulombic efficiency due to the undesired hydrogen evolution reaction (HER) that competes with the desired reduction of iron during charging. Second, they have a low round-trip efficiency (around 40%) due to this low Coulombic efficiency and a high overpotential during the charging and discharging cycle.
This means a significant amount of the energy required to charge an iron-air battery is lost and not available during the discharge of the battery, reducing the amount of energy that is actually stored. Further, this battery chemistry may be susceptible to anode corrosion, cathode clogging, and cathode poisoning from contaminants in ambient air. And unlike lithium-ion batteries, an iron-air battery has additional system complexity and balance of plant requirements for the air cathode.
Iron-air batteries also have a relatively low power density and poor rate capability, which means they are not well-suited for applications requiring rapid discharge. For these reasons, the majority of the capacity of an iron-air battery would not be accessible for diurnal cycling and would likely only be fully utilized 1-2 times per year, severely restricting their applicability.
Flow batteries, also known as redox flow batteries, are a type of rechargeable battery where energy is stored in liquid electrolyte solutions that are kept in external tanks, as opposed to conventional batteries where the energy is stored by electrodes within the battery cell itself.
Flow batteries consist of two separate tanks of liquid electrolyte solutions. The electrolytes are pumped from these tanks into a cell where they are separated by a membrane. One electrolyte acts as the cathode and the other as the anode. The electrochemical reactions take place in the cell. During the discharge phase (i.e., when energy is being supplied for an external device), electrons are transferred from the anode to the cathode, creating an electric current that oxidizes and reduces the electroactive species in the electrolyte on the respective sides of the cell. During charge, the electroactive species in the anolyte (anode side of the membrane) decreases oxidation state while that of the catholyte (cathode side) increases oxidation state. During the charging phase, an external power source is used to reverse this reaction, replenishing the electrolytes.
Flow batteries have a very long cycle life and minimal degradation over time because the energy is stored in the electrolyte rather than in the battery cell itself. Another advantage of flow batteries is that they can be left completely discharged for long periods without suffering any damage, which is not the case with many other types of batteries. They also have a quick response time.
Flow batteries have some downsides as well. Their energy density is significantly lower than lithium-ion batteries, meaning they take up more space for the same amount of energy stored. This makes them unsuitable for portable applications, or situations where grid storage is needed in urban or suburban areas. They can also be complex and expensive to manufacture and maintain, as the system involves pumps, sensors, and control units to manage the flow of the electrolyte.
Nickel Hydrogen Batteries
Nickel-Hydrogen (NiH2) batteries are a type of rechargeable battery that has been primarily used for satellite and space applications due to their robustness and long cycle life. Nickel-Hydrogen batteries consist of a positive nickel hydroxide (Ni(OH)2) electrode and a negative hydrogen electrode, separated by an alkaline electrolyte (usually potassium hydroxide). The battery’s energy is stored and released by the electrochemical reactions of the nickel hydroxide and hydrogen electrodes.
When the battery is discharging (providing energy to an external device), the nickel oxyhydroxide is reduced to nickel hydroxide and water is consumed at the positive electrode, and hydrogen is oxidized to form water at the negative electrode, generating electrons that flow through the external circuit. When the battery is being charged, these reactions are reversed. NiH2 batteries have a high specific energy and a long cycle life. They can endure thousands of charge-discharge cycles with minimal performance degradation, making them ideal for long-term applications like satellites. They’re also capable of operating over a wide range of temperatures. Despite the flammability of hydrogen gas and the associated risks of storing gases to pressures of up to 1200 psi, nickel hydrogen batteries are reported to have a good safety profile.
On the other hand, NiH2 batteries are more expensive than other battery technologies due to their complex construction. They also have a lower energy density compared to lithium-ion, and their charge-discharge efficiency is not as high. Both types of batteries have environmental considerations. Lithium-ion batteries have raised concerns due to the mining of lithium and cobalt (used in some lithium-ion chemistries), while nickel mining for nickel-hydrogen batteries also has environmental implications.
Liquid Metal Batteries
A liquid metal battery is composed of three layers: a top layer with a low-density liquid metal that serves as the positive electrode, a bottom layer of high-density liquid metal that serves as the negative electrode, and a molten salt layer in between that serves as the electrolyte. These three layers naturally settle into distinct strata based on their densities and immiscibility.
During the discharge phase, ions cross the electrolyte and cause an oxidation reaction at the negative electrode and reduction reaction at the positive electrode that provides electrons to the external circuit. During the charging phase, an external power supply is used to drive the reaction in the reverse direction, regenerating the original composition of the electrodes.
Liquid metal batteries can operate at high temperatures, which can minimize degradation and enable a long lifespan. Because the system is entirely liquid, it doesn’t suffer from the cycle-to-cycle capacity fade seen in many solid-state batteries. However, the technology also has some challenges. The high operating temperatures required to keep the metals and salts in a molten state can lead to significant energy loss and present engineering challenges. The choice of materials can also impact the battery’s voltage and energy density and the use of gravity to isolate the electrodes requires the system to maintain a certain orientation, predisposing it to stationary applications.
How Alsym Is Changing the Game
Alsym batteries are a non-toxic alternative to lithium-ion that avoid lithium and cobalt completely, and use water as the primary solvent in the electrolyte and in the manufacturing of the electrodes. Using readily available, inherently non-flammable materials including manganese and other metal oxides, Alsym batteries offer high performance at lower cost and risk than Li-ion.
Alsym batteries can be manufactured in the same facilities but at lower cost than lithium ion, allowing us to take advantage of existing infrastructure and industry knowledge. And while other battery technologies must be produced in expensive dry rooms and clean rooms and use toxic solvents that require recovery systems, our batteries can be built with less complexity and increased safety.
We’re working to make low-cost, non-flammable batteries available to all, in applications ranging from maritime shipping and electric vehicles to grid-scale energy storage. Contact us to find out more about the future of battery technology.