What can Replace Lithium Ion Batteries? Will the Four Hour Limit Mark the Beginning of Its Demise?

7 min readSep 16, 2020

Even if we don’t know what “lithium” and “ion” individually mean, we’ve surely heard of “lithium ion battery”. Today, the name has become the brand ambassador of battery industry and honestly, it deserves the fame. After all, lithium ion batteries are the current market leaders earning the title of “The King” from stingy experts. I won’t blame them as it is a befitting title considering the battery’s immense popularity. Furthermore, the battery price continues to drop every year. But no matter how good a technology is, it always has a weakness. As history shows, every king has fallen sooner or later irrespective of his might.

Don’t get the wrong idea! I’m not the evil guy who hates lithium-ion batteries and has an army waiting to take them down. Rather, their unique chemistry limits their usage in all applications, particularly in large-scale heavy duty commercial applications requiring enormous amounts of energy for long periods of time.

Can the dark horses — the next generation energy storage technologies replace lithium ion batteries? Let’s find out…

Why Should We Even Replace Lithium Ion Batteries?

Like I always say, every battery has its own set of disadvantages. The following list illustrates the problems with lithium ion batteries:

Fragile — The battery’s sensitivity to every small change in surroundings like temperature variations is uncanny. The experience is similar to handling a baby! Consequently, the output voltage fluctuates randomly and may not only damage the battery but the electrical equipment as well. Thus, they generally require complex electronic power management circuits (a mother/personal caretaker) like battery management systems to protect the battery and regulate its operation.
Cost — Whenever there is an issue in cost then rest assured that mass production is definitely a problem. They are about 40% more expensive than nickel-cadmium batteries thereby making its manufacturing process that much more costlier. This inhibits its application in the grid-scale usage for long duration storage (LDS).
Transportation of the Batteries for Trade — Battery industry has stringent regulatory policies for overseas and intra-continent transportation. The safety and travel policies governing the transportation of lithium ion batteries only raise the bar. For example, cargo airlines limit the weight and number of these batteries for safety purposes. Airlines strictly prohibiting inclusion of power banks (usually made of lithium ion batteries) in the check-in baggage is another example.
Ageing or Loss of Battery Capacity- According to a battery testing firm, Cadex Electronics, a fully charged lithium ion battery loses 20% of its capacity after one year of operation [1]. Moreover, the loss of capacity also depends on the cycle life or number of charge-discharge cycles.
The Four Hour Limit — They cannot store energy for more than four hours when used as energy storage for renewable energy sources. Typically, the preferred time period is in the order of a few hours or days and hopefully can be scaled up to months or even years.

The Dark Horses: Long Duration Storage (LDS) Technologies to Replace Lithium Ion Batteries

Both, the high cost and the battery chemistry together result in the four hour limit. So, what are the probable other choices that can replace lithium ion batteries? Presently, there are three technologies that are popular amongst the experts (in no order of preference):

Flow Batteries
Compressed Air Energy Storage
Thermal Energy Storage
Metal Air Batteries

Each of the above storage technologies do a very simple job. They redistribute energy to bridge the gap between energy supply and demand particularly with renewable energy sources in grid-scale applications. The next section describes each of the above energy storage technologies in detail.

Flow Batteries

Although the functioning is similar to a typical electrochemical cell, the different structure sets it apart from other commonly used batteries.

As shown in Fig 1, it is made up of two large chambers, each containing an electrolyte for the reaction. Now, the two electrolytes are pumped out of the chambers into a separate smaller reaction cell where the reaction takes place. Consequently, the smaller cell contains the electrodes connected to an external to generate electric current. As the reaction progresses towards completion, the electrolytes travel back to the large chambers. Since the electrolyte flows in and out of the chambers, it is called “flow batteries”.

Structure of a flow battery that could replace lithium ion batteries — Fig 1 — Structure of Flow Battery [2]

A good analogy is comparing the flow battery to the one in our cars. The large chambers act like the fuel tanks. So, we refill the electrolytes in the chambers the same way we refill the gasoline, petrol or diesel in the fuel tanks. And, the reaction cell is similar to the internal combustion engine that converts energy from an unusable form into a usable form.

The primary reason flow batteries are suitable for long duration storage is because of the large size of the tank-like chambers and the availability of the electrolytes. Thus, it can generate current for as long as the electrolyte flows into the reaction cell. To put it formally, this battery recharges from the renewable energy sources and then discharges as per our need.

Moreover, it does not degrade with the number of charge-discharge cycles so it offers a highly competitive price per MWh in four-hour-plus applications. They also have low operations and maintenance costs. At the same time they offer comparable response times to lithium-ion batteries while having a round-trip efficiency that is only slightly lower [3].

Compressed Air Energy Storage (CAES)

Firstly, to simplify the physics, it is important to note that air compression generates a lot of heat.

The excess or off-peak energy from the renewable energy sources is used to compress air which is then stored away, often in an underground tank. The heat from compression was dissipated into the atmosphere thereby resulting in energy wastage as well as production of carbon dioxide, a greenhouse gas. Modern Advanced CAES (A-CAES) systems as well as Liquid Air Energy Storage Systems (LAES) store this heat and use it to expand the compressed air when required. The expanded air then passes through an air (or gas) turbine that generates electricity from the flow of air.

Fig 2 — Compressed Air Energy Storage Construction [4]

The CAES systems are retro-fittable which means they can be easily installed and combined with other existing storage technologies. They can store energy for more than 24 hours thus making them a good a choice for long duration storage. According to Hydroster, a company using A-CAES technology, the shelf-life of the systems is more than 30 years. Adding another feather to the cap — these systems can last long with low maintenance costs.

Thermal Energy Storage (TES)

As the name suggests, thermal energy storage systems store energy in the form of heat. Unlike the A-CAES where the heat supplements compression, in thermal energy storage, heat is the primary store. A working fluid (or thermal store) is a special material that absorbs and stores heat energy. The three types are:

Sensible Heat Storage — The material stores heat by elevating its temperature. When required, we cool the material and extract the heat to generate electricity.
Latent Heat Storage — The material undergoes a phase change during the process. In other words, it melts/solidifies/evaporates/condenses to release or store the supplied heat energy.
Thermochemical Heat Storage — A reversible endothermic chemical reaction occurs to form products that store the heat. When these new products convert back into the original reactants, they release the stored solar energy.

Concentrated solar power plant (CSP) is an example of thermal energy storage system as it collects the sun’s heat onto a thermal receiver. The material then stores the heat received from the thermal receiver. The heat from the thermal store drives a turbine to generate electricity. For more details on the categories, you can read my article on Concentrated Solar Power and Thermal Energy Storage.

The primary advantage is that thermal energy storage systems are cheap and provide at least 70% efficiency in the worst case. Moreover, they are safer and make a great choice for harsh environments. They are a great choice to replace lithium ion batteries.

Metal Air Batteries

Another electrochemical cell with a structural difference. Unlike flow batteries, metal air batteries are more closer to our everyday battery. The anode is made of a pure metal like zinc, aluminum, lithium, etc. However, this battery uses an external cathode that is in contact with the surrounding air. In simple words, the cathode is not sealed thereby allowing the ambient air to take part in the chemical reaction.

Zinc-air and iron-air batteries are popular examples for long duration grid-scale energy storage. Although not as competent as its competitors, it still a better choice when compared to a lithium ion battery. The primary challenge hindering its usage is the anode metals.

Conclusion

Flow batteries, CAES and thermal energy storage are gigantic systems. Hence, they demand large spatial area that further requires a rigorous geological and cost analysis. It is more of a question of accessibility of sites to setup plants, manufacturing factory elements, materials and the distance from grid as well as the renewable energy sources.

Furthermore, the initial investment is high. However, the good news about systems requiring large initial investments is that the technology usually runs for longer time periods in order of decades — a desirable outcome for these type of storage technologies.

The long duration storage technologies have not yet become a hot topic simply because they have not penetrated deep enough. But this doesn’t necessarily mean they will not! With sufficient financial investment and trust, they have the potential to transform how we store energy and supply electricity to cities.

Who knows, we might even have one that can be installed in our house!

Thank you for your time!