Solid State Batteries
Basics of Solid State Batteries Explained
Solid State Batteries (SSB) represent a revolutionary advancement in energy storage technology from hand-held consumer electronics through to electric vehicles, (EVs). Since the advent of modern lithium-ion cells and batteries more than 30 years ago, manufacturers have been busy creating advanced solid-state electrolytes which offer faster recharging times, better thermal safety, as well as much higher power densities.
Unlike traditional lithium-ion primary batteries that use a liquid electrolyte (a substance between a batteries electrodes which can pass an electric charge), solid-state batteries use a solid electrolyte material to conduct ions between their positive and negative electrodes. This fundamental design change from a liquid electrolyte to a solid separator offers several significant advantages.
What Are Solid State Batteries?
Solid State Batteries are another type of electrical battery which use a solid-electrolyte material between their positive and negative electrodes. This solid construction eliminates the risk of leakage, gases and thermal runaway which can cause fires in conventional lithium-ion batteries.
There exist many types of batteries, both primary and secondary. Primary batteries are simply single use batteries which once fully discharged cannot be recharged or used any more but must be discarded or recycled. This is because the chemical reactions that occur inside them to produce an electric current are irreversible once exhausted.
Secondary batteries like deep cycle batteries are rechargeable, so they can be used many times over again. In the case of EVs, PHEVs and portable handheld devices using secondary batteries makes the most sense, because utilising single use primary batteries in these types of applications seems unreasonable.
A battery is a device that converts the chemical energy contained within its plates directly into electrical energy by means of an electrochemical reaction. But only when its terminals are connected to an external closed circuit.
The term battery is now commonly used for all types regardless of whether it is a single-cell button type device or a multiple cell device. However, the basic electrochemical unit of a battery is the Cell.
Batteries and Cells
The main distinction made between a battery and an electrochemical cell lies in their composition. A “cell” is basically an assembly of electrodes and an electrolyte that allows for the flow of ions between them. While a “battery”, either primary or secondary, is defined as a collection of cells. Then we can correctly say that an electrochemical cell is the fundamental building block of a battery.
Bog-standard batteries, such as a standard 12 volt automotive battery consist of many electrochemical cells sandwiched together with each cell consisting of a positive plate (Cathode), a negative plate (Anode) and an electrolyte. These cells are electrically connected together in appropriate series or parallel arrangements to achieve the required terminal voltage and current capacity. Then a battery is a self-contained, commercially available power source.
Typical Liquid Electrolyte Battery Construction
Here in this simple example, the battery consists of four electrochemical cells. Each 3.6 volt cell is electrically connected in series to provide the required 14.4 volt open-circuit voltage. The electrolyte provides the medium for the transfer of electric charge (as ions) inside the cell between the anode and cathode. In this example the electrolyte, which must have good ionic conductivity, is shown as a liquid. For example, water or a gel with dissolved salts, acids or organics added to improve its ionic conductivity.
Then we can see that electrochemical cells and therefore complete batteries are identified as primary (non-rechargeable) or secondary (rechargeable), depending on their ability of being electrically recharged. Clearly, the ideal battery (or cell) is one that is inexpensive, safe to use, and has infinite energy storage capability.
However in practice, electrochemical batteries such as zinc-carbon, zinc-chloride batteries, can have a short shelf-life, low energy densities, low efficiency under high current discharges and have a terminal voltage which falls steadily with discharge. Even automotive batteries can have a low energy-to-weight ratio. So solid electrolyte batteries which use silver, lithium, or aluminium metal electrodes are now being developed.
We have seen that batteries can have a liquid, gel, or an absorbent paper material (these are termed “dry cells”) as there ionic electrolyte in both primary and secondary batteries have been available for many years, so understanding batteries like these is relatively simple. Today, solid state batteries with a lithium metal electrodes and a solid polymer electrolyte are considered the next generation of high energy battery technology for electric vehicles and transportation.
Solid State Electrolyte Batteries
Solid State Batteries (SSB) is a technology that has the potential to change the way we store and use energy. Unlike traditional batteries, which use a liquid or gel-type electrolyte to transfer ions between the electrodes, solid state batteries use a solid electrolyte that separates the electrodes. This solid state separator provides many advantages over its liquid counterparts by offering a higher terminal voltage and energy density for a given size.
Basically, the working principle of solid state batteries is very similar to that for a conventional battery which has a liquid or semi-liquid electrolyte. For example, lithium-ion batteries which are widely used in electric vehicles (EVs).
What is different is that solid-state lithium-metal batteries have a solid state separator as well as a lithium metal anode reducing the risk of volatile and flammable liquid-based electrolytes.
The use of a solid state separator results in the carbon anode used in standard lithium-ion batteries to be replaced with a lithium-metal anode. A lithium metal anode is more energy dense than conventional anodes increasing energy density and faster charging times relative to its size or weight. Also, the use of lithium-metal anodes and high-voltage cathodes allows for increased cell voltages, thereby enhancing the battery’s energy density.
Construction of Solid State Batteries
Here, the electrode materials serve as the energy storage devices for metallic lithium within the secondary battery. A solid electrolyte made from specialised polymers, oxides, or sulphide-based materials serves as the separator, with the cathode made of lithium-based intercalation (insert) compounds such as lithium nickel manganese cobalt oxide (NMC) or lithium iron phosphate (LFP).
Positioned between the two electrodes, this solid electrolyte plays a crucial role with regards to ionic conductivity and chemical compatibility with the electrodes. The solid electrolyte must conduct lithium ions efficiently while also physically separating the two electrodes to prevent them touching resulting in internal short circuits.
How Do Solid State Batteries Work?
The operation of solid-state batteries is based on the movement of lithium ions between the anode and cathode electrodes during normal operation of charging and discharging. During discharge (connected to an external circuit), the lithium metal at the anode releases positively charged lithium ions (Li+), which migrate through the solid electrolyte toward the cathode, where they are stored by intercalation.
At the same time, negatively charged electrons (-e) flow through the external circuit, providing electrical energy to power the connected circuit and/or devices. During charging, (connected to a charger) this process reverses direction with the charging voltage driving the lithium ions back through the solid electrolyte before being deposited once again onto the lithium metal anode. However, this process is more complex than in normal lithium-ion (Li-ion) batteries because of the unique behaviour of both the solid electrolyte and lithium metal anode.
Back at the batteries anode, these lithium ions reattach themselves to the surface of the existing lithium metal in a uniform and controlled manner and is a critical aspect of charging solid state lithium metal batteries. Ideally, the lithium should deposit smoothly and evenly to create a flat surface. However, if it is uneven or occurs in isolated spots, this can lead to the formation of lithium dendrites needle-like structures which could grow through the solid electrolyte causing a short circuit and battery failure.
Then we can see that the solid electrolyte/separator of a solid state battery plays an important role in preventing failure. Certain solid electrolytes, especially ceramic materials, possess high mechanical stiffness, which can physically suppress the growth of dendritic crystals and needle-like lithium structures which could penetrate the battery’s separator. However, its effectiveness depends on many factors including fast charging density and temperature which can increase the likelihood of uneven lithium deposition and dendrite formation.
Also another issue during charging is in maintaining a good physical contact between the lithium metal and the solid electrolyte. Unlike liquid electrolytes that can flow and fill any gaps, solid electrolytes are not suited to changes in volume easily. Thus, as the lithium reattaches itself back onto the anode, voids or cracks can develop, which can restrict electron and ion flow degrading performance over time. The use of buffer layers, soft electrolyte composites, or applying external pressure during battery operation can help reduce this issue.
Tutorial Summary
We have seen here in this tutorial about solid state batteries that batteries are basically electrochemical storage devices that convert their stored chemical energy into electric energy, and depending on the specific type of the electrochemical process and electrolyte materials used, they can be classed in a number of ways.
Today, solid state batteries (SSB) with a lithium metal electrode are considered the next generation of high energy battery technology making them the possible successor of Lithium-ion batteries. Solid-state lithium metal batteries offer several advantages with the development of polymer based solid state batteries with a metal electrode is well advanced and being used in electric vehicles (EVs), eBikes and scooters.
However, there are still some technical challenges to overcome before these solid state batteries can be widely adopted. Suppressing the growth of dendrites needle-like lithium deposits that can cause short circuits and better performance in high-temperature environments as well as a longer charge/recharge cycle life under certain conditions is key to enabling reliable, fast-charging solid-state batteries for long term commercial applications.
Despite these challenges, solid-state lithium metal batteries are considered one of the most promising paths forward for next-generation energy storage, particularly for electric vehicles, portable electronics, and grid storage applications with many leading companies continuing to push the boundaries of this technology.
The solid-state battery vs lithium-ion battle will continue to grow, but as batteries with a lithium metal anode in combination with solid state electrolyte continue to be developed while using non-flammable high-temperature resistant materials to enhance the battery’s safety performance. “Solid State Batteries” might just be be the successor to Li-ion batteries.
To learn more about solid state batteries and the use of lithium metal anodes in combination with solid state electrolytes, or maybe you just want to obtain more information about battery energy storage systems in general and how you can use them in your home. Then find your ideal book about solid state battery systems today direct from Amazon and understand how you can use battery storage technologies to power your home.
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