Anode-less Lithium Metal: A Gateway to Maximizing Energy Density
Lithium metal batteries will form a significant portion of next-generation electric vehicle batteries. However, increasingly, lithium metal battery developers are taking the anode-less approach, constructing cells without lithium metal foils at the anode to reduce costs. So-called 'anode-free' batteries are electrochemically equivalent to lithium metal batteries but are constructed with no excess lithium. Instead, the anode active material is deposited on the anode current collector during the first charge and is sourced from the cathode (which is also the case for a cell with a graphite anode). Anode-less designs are poised to become a primary focus of commercialization for lithium metal battery developers. For more information, see IDTechEx's recent report: “Lithium Metal Batteries 2025-2035: Technology, Players, and Forecasts“.
As with typical lithium metal batteries, lithium metal plates onto the current collector during charging and is stripped during discharging through the transfer of lithium ions through the electrolyte. However, cells are constructed without excess lithium metal for anode-less batteries, so there is no lithium metal on the anode current collector before the first charge occurs. As a result, the deposition of the first charge is even more important. Lithium must plate onto the current collector evenly, and there cannot be significant losses; otherwise, the battery stability will be significantly impeded.
Structural designs of lithium metal cells. Source: IDTechEx
An anode-less design has two main advantages: energy density and costs. Energy density is improved as there is a higher volume of active material in the cell (aka, no excess lithium which does not play a role in generating power). Costs can also potentially be reduced, as cells can be constructed without lithium metal foils, which are expensive and difficult to produce as a result of the required thinness. However, there are challenges associated with the development of anode-less cells. As with conventional lithium metal batteries, anode-less cells frequently exhibit dendrite growth, which can reduce battery lifetime. This is an even more significant problem for anode-less cells, as there is no excess active material. Without excess active material, material losses to irreversible lithium plating have an even greater effect on the battery performance, as there is no excess to compensate for losses. As a result, anode-less cells can experience challenges achieving competitive cycle life.
Solutions to dendrites
Outside of changing environmental working conditions, there are three main approaches to modifying battery design directly in order to improve lithium metal battery lifetime, which are especially important for anode-less cells:
- Mechanical blocking: Physical barrier layers can be used in order to limit dendrite growth and prevent dendrites from reaching the electrolyte. This could mean harder separators or separator coatings. However, the separator must still be constructed such that ions can flow between electrodes.
- Ion transport regulation: Regulation of ion transport can help to encourage more homogeneous lithium deposition and stripping. This could mean the use of a gel or ceramic electrolyte, either as a coating or instead of a liquid electrolyte. This serves to improve conductivity at the 'skeleton' of the separator (i.e., the rigid lattice between pores). A 3D separator can serve the same purpose, though it may be more expensive.
- Deposition regulation: Direct regulation of deposition is of primary importance for ensuring homogeneous plating and stripping and preventing dendrite formation. This can mean modification of the current collector or the separator, in both cases, to create a 3D lattice of nucleation sites, which lithium ions are especially attracted to, directly controlling where lithium ions are deposited. Examples include the use of carbon nanotubes in cylinder structures.
Players
There are many companies working in the anode-less lithium metal space. However, for many companies, it is hard to achieve completely anode-less cells – instead, low excess metal is pursued. Some examples are included below:
- Ensurge Micropower: Ensurge has developed anode-less cells for use in micropower applications.
- QuantumScape: QuantumScape are developing lithium metal cells without an anode. A solid-state separator is used to separate the anode current collector from the catholyte solution, whereby the cathode material is suspended in a liquid organic electrolyte.
- Our Next Energy (ONE): Our Next Energy has developed anode-less cells, which are used in a dual-battery system for electric vehicles. Conventional graphite-anode cells are used for the majority of the energy requirements, while anode-less lithium metal cells are used for longer journeys, thereby circumventing cycle life challenges.
Key takeaways
Anode-less cells are expected to become a primary focus for commercialization by lithium metal battery developers as a result of the enhanced energy density associated with them. Challenges associated with their development are the same as for conventional lithium metal cells but exacerbated by the lack of excess metal. As a result, the successful development of cells with higher excess metal could also lead to new innovations for anode-less cells. IDTechEx predicts anode-less designs to be a significant proportion of the future market and provides more detail in its recent report: “Lithium Metal Batteries 2025-2035: Technology, Players, and Forecasts“.
To find out more about this IDTechEx report, including downloadable sample pages, please visit www.IDTechEx.com/LMB.
For the full portfolio of energy storage and batteries market research available from IDTechEx, please see www.IDTechEx.com/Research/ES.
