In recent years, there has been growing interest and development in solid-state lithium batteries, marking an important milestone on the road to electrification. These batteries offer a number of advantages compared to conventional lithium batteries, such as higher energy density, greater safety and a longer service life.
The structure of a lithium-ion battery.
The image below shows the structure of an actual lithium-ion cell, the technology now used in the vast majority of electric vehicles on the road. What are we looking at?
Lithium-ion batteries are an advanced battery technology that has four main components: anode, cathode, separator and electrolyte.
Each lithium-ion cell consists of:
- Two electrodesThe cathode and anode accept the intercalation of lithium ions within their structure:
- A cathode o positive pole of the battery made of cathodic material (LFP, NMC, LMO, etc.)
- A anode o negative pole made of anodic material (carbon or graphite)
- The central separator is a thin layer of plastic polymer (polyethylene or polypropylene) that prevents direct contact between the two electrodes, allows the flow of lithium ions and acts as an insulator.
- The electrolyte is usually a solution of lithium salts in an organic solvent, fills the entire volume inside the cell, soaks the electrodes and allows for conduction of lithium ions between the electrodes during charging and discharging of the cell.
These components are critical to the operation of lithium-ion batteries and their ability to store and release energy efficiently.
The structure of a solid-state battery
The structure of a solid-state battery differs from a conventional lithium-ion battery. Instead of using liquid or gel electrolytes, solid-state batteries use solid electrolytes to facilitate the flow of lithium ions.
In a typical solid-state battery, the following main components are found:
- Cathode: The positive electrode of the battery, where the reduction reaction occurs during discharge. In solid-state batteries, the cathode may be composed of materials such as metal oxides, sulphides or phosphates.
- Anode: The negative electrode of the battery, where the oxidation reaction occurs during discharge. Like the cathode, the anode in solid-state batteries can be made of materials such as graphite, silicon or lithium metal.
- Solid electrolyte: A solid material that acts as an ionic conductor in the battery. Solid electrolyte allows the transport of lithium ions between the cathode and anode during charging and discharging. Examples of solid electrolytes are ceramics, conductive polymers or ionic glasses.
- Separator: A layer or membrane placed between the cathode and anode to avoid direct contact between them and prevent short circuits. The separator also allows the flow of lithium ions while maintaining the physical separation between the electrodes.
The structure of a solid-state battery can vary depending on the specific design and materials used. However, the presence of a solid electrolyte rather than a liquid electrolyte is the key feature that distinguishes solid-state batteries from conventional lithium-ion batteries. This approach aims to improve the safety, energy density and stability of batteries, opening up new possibilities for applications in electronics, mobility and energy storage.
Figure 2] [Figure 2
The grey centre layer in a solid-state battery corresponds to the solid-state separator. The solid-state separator is a thin, solid layer that is placed between the cathode and anode in the battery structure.
This solid-state separator layer plays a crucial role in battery performance by allowing the movement of lithium ions between the electrodes during charging and discharging. In addition, by preventing direct contact between the cathode and anode, the separator prevents short circuits and improves battery stability and efficiency.
How does a solid-state battery work?
When the cell is charged in a solid-state battery, lithium ions move from the cathode to the anode through the separator. During this process, lithium particles pass through the separator structure and accumulate between the separator itself and the anode electrical contact, forming a solid layer of pure lithium. This results in the anode being composed solely of lithium particles and having a smaller volume compared to a lithium-ion technology anode using a graphite structure.
What are the current strengths in solid-state battery technology?
While solid-state batteries look promising in terms of energy density, durability and safety, it is important to keep in mind that this technology is still under development. So far, lithium-ion batteries remain the most advanced and widely available technology on the market.
Several variants of lithium-ion batteries exist, each designed for different applications, and are produced in large quantities. While solid-state batteries have the potential to outperform lithium-ion batteries in the future, advances and improvements are still required before they are ready for wide-scale adoption.
Having said that, let's take a look at the advantages of solid-state batteries:
- The key safety factor
In the development of solid-state batteries, safety is a key priority factor. Solid-state batteries offer significant improvements in terms of safety compared to conventional lithium-ion batteries using liquid electrolytes.
The use of solid electrolytes in solid-state batteries eliminates the risk of leakage or spillage of flammable liquids, which significantly reduces the risk of fire or explosion. In addition, by eliminating flammable materials, the possibility of unwanted chemical reactions that could compromise safety is reduced.
Another important safety advantage of solid-state batteries is their increased resistance to dendrite formation. Dendrites are filamentous metal growths that can form in conventional lithium-ion batteries and can cause short circuits and battery malfunctions.
In solid-state batteries, the solid structure of the electrolyte helps prevent or limit the formation of dendrites. This is because the solid electrolyte provides greater uniformity and stability compared to the liquid electrolytes used in conventional batteries. As a result, solid-state batteries have a higher short-circuit resistance and greater durability under extreme operating conditions.
However, it is important to note that the safety of solid-state batteries is still under development and more research is needed to address potential challenges and ensure their safe operation under various conditions and applications.
- Record energy density
Solid-state batteries have the potential to offer higher energy density compared to conventional lithium-ion batteries. Energy density refers to the amount of energy that can be stored in relation to the volume or mass of the battery.
Due to their design and the use of advanced materials, solid-state batteries have the ability to store a greater amount of energy in a smaller space. This means that greater energy storage capacity can be achieved in a more compact size, which is beneficial for portable devices, electric vehicles and other applications where space is limited.
According to recent studies, solid-state batteries have been found to have an energy density potentially 2-2.5 times higher than current lithium-ion technology. This significant difference in energy density would enable the development of lighter and more compact batteries, which would benefit electric mobility by providing greater range and reducing the weight of vehicles.
The higher energy density of solid-state batteries allows for greater range and efficiency in electric vehicles, as they can store more energy in a smaller space.
3. Ultra-fast loading times
Solid-state batteries also show promising ultra-fast charging times compared to conventional lithium-ion batteries, up to six times faster. Due to their design and composition, solid-state batteries can withstand higher charge rates without experiencing significant degradation.
This means that devices and vehicles equipped with solid-state batteries could be charged much faster, resulting in significantly reduced charging times compared to today's batteries. This is especially relevant for electric mobility, where users want to minimise downtime and enjoy fast and convenient charging.
4. Faster production
Solid-state batteries also have the potential to offer faster production compared to current battery technologies. Due to their simplified design and the elimination of liquid components, solid-state batteries can be easier and faster to manufacture.
The absence of liquid electrolytes reduces the complexity of the production process and eliminates the need for filling and sealing stages. This can significantly speed up the production line and increase overall efficiency in solid-state battery manufacturing.
In addition, solid-state batteries can offer greater uniformity and consistency in terms of performance and characteristics. This means that there is less variability in the properties of individual cells, which facilitates the process of matching and assembling batteries.
However, it is important to note that, although improvements in production speed are expected, solid-state battery technology is still under development and has not yet reached a large-scale production stage. Further research, development and optimisation is required to ensure fast and efficient large-scale production of solid-state batteries.
Challenges facing solid-state batteries
While solid-state batteries have the potential to revolutionise the automotive industry and improve the efficiency of electric vehicles, it is important to note that this technology is still at an early stage of development and faces several challenges before widespread adoption.
However, it is expected that with time and technological advances, these limitations will be overcome and solid-state batteries will become a reality in various fields of application.
- Stability problems
One of the main challenges facing solid-state battery technology is long-term stability. As batteries are repeatedly charged and discharged, they can experience degradation in performance and capacity. In the case of solid-state batteries, this is partly due to the interaction between the materials used in the battery structure, such as the electrodes and the separator.
The materials used in solid-state batteries must be stable enough to withstand charge and discharge cycles without significant degradation. In addition, they must resist unwanted chemical reactions that can lead to dendrite formation, short circuits or even catastrophic failure.
To address these stability issues, researchers are exploring different approaches. These include improving the materials used in the battery structure, such as finding more stable solid electrolytes and optimising electrodes to reduce degradation. New design and manufacturing approaches are also being investigated to improve the stability and durability of solid-state batteries.
- Separator only works at high temperature
In solid-state batteries, the movement of ions is facilitated by the presence of a solid electrolyte that allows ionic conduction. However, this solid electrolyte may have limited ionic conductivity at lower temperatures, which affects battery performance under normal operating conditions.
Currently, the solid electrodes in solid-state batteries perform optimally at temperatures above 50 degrees Celsius. This means that in real-world applications, where batteries will not always be in a hot state, battery performance may decrease significantly.
To make solid-state batteries more viable and practical, progress is needed in the development of solid electrolyte materials that can operate efficiently at lower temperatures. This would enable better battery performance over a wider range of temperatures and their application in a variety of devices and vehicles without temperature restrictions.
Researchers and scientists are working on the development of improved solid electrolyte materials that can offer higher ionic conductivity at lower temperatures. Overcoming this challenge will allow the full benefits of solid-state batteries to be realised and open up new opportunities for their deployment in a variety of applications, including electric vehicles.
- Life cycles are still short
Solid-state batteries currently being tested have shorter life cycles compared to other lithium-ion technologies.
The main challenge lies in achieving good contact between the cell layers, as loss of contact negatively affects battery capacity and performance. Researchers are working to improve the stability of the layers, using improved contact materials and more precise manufacturing techniques.
- High cost
A significant challenge in the implementation of solid-state batteries is their high cost. Because this technology is still under development and is not produced on a large scale, the materials and processes used to manufacture solid-state batteries are expensive. In addition, significant investment in research and development is required to improve efficiency and reduce production costs.
However, as technology advances and economies of scale are achieved, the costs of solid-state batteries are expected to decrease, making them more affordable and viable for a variety of applications in the future.
Main fields of application
Solid-state batteries have a wide range of application fields. One of the main sectors is the electrification of transport. These batteries promise to increase the range of electric vehicles, reduce charging times and improve safety. This could drive mass adoption of electric vehicles and contribute to the reduction of greenhouse gas emissions.
In addition to transport, solid-state batteries can also be used for large-scale energy storage. This would allow intermittent renewable energy sources, such as solar and wind, to be more effectively integrated into electricity grids, providing stability and reliability.
In the field of portable electronics and mobile devices, solid-state batteries could significantly improve the battery life and performance of smartphones, laptops and wearable devices, offering greater convenience and autonomy to users.
These batteries could also drive advances in the efficiency and capacity of household appliances and electronic devices in the home, such as smart appliances, home energy storage systems and electronic entertainment equipment.
Another potential field is space technology, where solid-state batteries could be used in space missions due to their higher energy density, safety and resistance to extreme conditions.
These are just a few examples of the application areas for solid-state batteries. As this technology continues to develop and overcome its challenges, new opportunities are likely to open up in a variety of sectors, with electric vehicles being one of the key drivers of this innovation.
Although solid-state lithium batteries are still in a developmental stage and are not widely available on the market, they are expected to play an important role in electrification as they are refined and become more affordable. Their potential to revolutionise the energy and mobility industry is promising, driving a more sustainable and emission-free future.