future of energy storage

Energy is a fundamental requirement for the world to function and it forms the bedrock on which almost all other technology functions. At present, we are heavily dependent on unsustainable sources of energy to meet our consumption needs. Hence, a shift towards harnessing more sustainable forms of energy is a must. Sustainable energy sources like solar or wind is abundantly available but comes at the cost of being intermittent i.e. discontinuous which is a major disadvantage over current fossil-based energy sources. A key enabler in order to smoothly shifting towards sustainable energy sources is adopting effective energy storage methods that can make up for the intermittent nature of sustainable energy sources. Lithium-ion batteries currently serve as the dominant energy storage method owing to its rechargeable nature and high energy density. Let us get a little technical and dive a bit deeper into the functioning of a lithium-ion battery. Lithium has a high propensity to lose an electron and easily create an electrochemical potential difference making it a very suitable element for making batteries. Lithium-ion battery chemistry includes a lithium metal oxide cathode (+ve terminal) and graphite sheets in the anode (-ve terminal) filled a lithium-ion electrode and a separator. While charging, the electrons of the lithium metal oxide cathode get removed leaving positively charged lithium ions to move internally through the electrolyte past the separator and get interleaved between the graphite anode sheets. The electrons extracted from the cathode while charging move externally (i.e. the outside the battery) to the anode. So, in a charged state, lithium ions and electrons are interleaved in the graphite anode sheets in such a way that they cannot recombine internally within the anode. This causes a potential difference as lithium ions are unstable and they need a way to recombine with electrons to reach a stable state. This is exactly what happens when the battery is connected to a load (for e.g. motor), the electrons in the anode seek an external path (i.e. outside the battery) through load (which is what we observe as electrical current) to reach the cathode as it cannot move internally within the battery as the separator only allows the passage of lithium ions. As electrons stored in the anode migrates externally towards the cathode, the lithium ions migrate internally within the battery by passing through the separator to reach the cathode and recombine with the electrons and reduce the potential difference. However, lithium-ion batteries come with a few issues: firstly, there are supply chain constraints as availability of lithium is restricted to very few areas globally which can cause concerns from the point of view of economics and secondly, lithium-ion batteries have a safety concern due to its high energy density making it highly susceptible to overheating and fires. Uncovering new and innovative storage technologies is crucial to effectively harness energy from sustainable energy sources. I have been actively learning about potential energy storage technologies of the future to help enable our transition into a more sustainable future and came across quite a few noteworthy energy storage technologies which I have penned down below:

sodium-ion batteries: This battery technology is very similar to lithium-ion batteries except that the lithium component is replaced by sodium. Sodium is more abundantly available than lithium and hence can be a good hedge to the supply chain constraint posed by lithium-ion batteries. Sodium however has lower energy density as it has a lower propensity to lose electrons in comparison to lithium. Hence, sodium-ion batteries will be relatively bulkier than lithium batteries making it more suitable for large-scale stationary energy systems (SES) rather than portable systems.
solid state batteries: This technology is an incremental improvement over lithium-ion batteries where the liquid electrolyte is replaced by a solid electrolyte. The advantage of solid-state batteries is that it can pack more energy into much a smaller area making it highly suitable portable energy storage systems (like EVs or electronics) which require spacial efficiency. The challenge with solid state batteries however is that they are hard to manufacture do which it is still in a very nascent stage of adoption.
flow batteries: This is a very interesting variation of conventional batteries where the electrolyte is stored separately from the cell. Flow batteries use separate tanks to store cathode electrolyte (i.e. catholyte) and anode electrolyte (i.e. anolyte) which is pumped into central cell system that holds the electrodes and where the electrochemical reactions take place. Flow batteries are bulky and hence mainly suitable for large scale stationary energy storage. A key advantage of flow state batteries is its optional scalability feature due to its detached structure where we can ad hoc alter the energy capacity of the battery by parallelly adding additional electrolyte tanks or central cells. Additionally, flow batteries are far safer than lithium ions batteries as the stored is distributed over a larger volume which prevents overheating.
gravity batteries: This is a very interesting way to store energy coming from intermittent energy sources by converting it into gravitational potential energy which can be later converted into electrical energy. There are a few different ways to create a gravity battery. One way is the hydro route where energy coming from intermittent sources is used to power a hydro pump that enables storage water at an elevated level which be released at a later time to power a turbine at generate electricity. Another conception of the gravity battery involves high elevated crane-like structures that use energy from intermittent sources to power motors which lift heavy blocks to a high elevation storing it as potential energy which can be released to convert them back into electrical energy when needed.
thermal batteries: This is again a very interesting type of energy storage technology. In thermal batteries, the energy coming in from intermittent sources is used to power an electrical heater that heats matter which has high capacity to store and retain heat energy like graphite (solid carbon batteries) or sand (sand batteries). These batteries can store heat up to temperatures like 2000 degree Celsius which can later be directly reused in heat-related processes in factories or indirectly to power steam turbine and generate electricity.
air batteries: compressed-air battery technology uses energy coming in from intermittent energy sources to power an air pump that compresses air into a high-pressure chamber which can be stored for a long duration and released into a low-pressure environment when needed to power a turbine that can be used to generate electricity. This technology however has low energy efficiency due to loss of heat that occurs when air is in its compressed state. Coupling air batteries with thermal batteries can be an effective way to preserve heat and maintain better energy efficiency.