Since they were commercialised in the 1990s, Lithium-ion Batteries (LIB) have been widely adopted as the main energy storage system in many applications, such us portable electronics.
During the last three decades, the technology has been developed progressively improving its properties and particularly aiming for higher practical energy density values. Such improvement, along with the need for a global transition towards a more sustainable mobility model, has made LIBs also the best choice for electric vehicles (EVs). LIBs development, though, is reaching the theoretical limits, meaning that alternative battery technologies need to be developed to meet the performance demands of automotive industry.
Several options are on the table, among which Lithium Metal Batteries (LMB) stand out for the higher gravimetric and volumetric energy density that Lithium Metal Anode (LMA) offers as negative electrode.
Nevertheless, LMBs are not free from their own limitations. Beyond the challenges in terms of constant LMA degradation in conventional liquid electrolytes during cell operation that limits the lifetime of LMBs, the use of metallic lithium prompts safety concerns and difficulties for the processing during cell assembly. In case of malfunction or thermal event of the cell, the presence of metallic lithium would make the process more dangerous, as was already demonstrated when LMBs were removed from market after being initially commercialized in the 1980s.
Besides, the chemical and mechanical properties of metallic lithium make the manipulation of this material challenging and costly.
Therefore, the development of LMBs without metallic lithium in the negative electrode when the cell is assembled would be highly desirable from the manufacturing point of view, and very promising from the commercialization and application standpoint. This concept, known as anode-less or anode-free, has attracted increasingly the attention of the battery community lately.
How can batteries work without the anode?
Conventional intercalation cathodes used in LIBs contain the lithium source in their structure when the cell is assembled. The same is the case for intercalation cathodes under development for next generations of LIBs (including both liquid and solid configurations), which are also the usual choice for LMBs.
In spite of the existence of some exceptions (technologies such as Li-S or Li-air batteries), this means that LMA works actually as an additional lithium reservoir to compensate for lithium losses originating from inefficiencies during electrochemical operation of LMBs. Hence, if efficiency is considerably improved, the need for an additional lithium source would be eliminated, and, thus, anode-less cells could be assembled and operated during extended cycle-life.
Advantages of anode-less batteries
Anode-less batteries offer a wide range of benefits that make them a very attractive alternative to LMBs. Firstly, the fact that LMA is avoided, maximises the gravimetric and volumetric energy density since there is no lithium excess in the cell. As above-mentioned, the lithium source is within the cathode and the metallic lithium layer would be deposited in-situ in the cell during the charge process upon cycling.