Are solid-state batteries really “the next big thing”? Where can the solid-state battery convince? And in which areas are there weaknesses? This article provides an overview.
There are many expectations that solid-state batteries will be superior to today’s energy systems. But how superior is this technology really? In this article, a comparison is made between solid-state batteries and conventional Li-ion batteries. Since there are different variants of solid-state batteries and Li-ion batteries, a total of four different cell concepts are compared. It will be several years before solid-state batteries are ready for series production (see [1]) and Li-ion batteries will also continue to develop. Therefore, the current status of the two technologies is not considered, but the predicted development status for 2028 is used as a basis.
Li-ion batteries 2028
For the Li-ion battery, two main developments are expected by 2028: For cathodes, the NMC (nickel manganese cobalt) cathode will continue to dominate, with nickel increasing from 50-60% today to 70-80%, and cobalt and manganese being used correspondingly less (NMC811 is expected to reach marketability, displacing NMC532 in the medium term). [2]
Graphite is generally used for the anode nowadays. It is expected that small amounts of silicon will be added to this in the future, enabling higher energy densities to be achieved. The proportion of additional silicon is expected to increase steadily over the next few years. [2]. No far-reaching changes are expected in the area of electrolytes. Although research is being carried out into the further development of today’s electrolytes, the focus here is primarily on the addition of additives [2], for example to reduce the risk of fire or to increase the dielectric strength [3].
Solid-State Batteries 2028
An outlook on the technology of solid-state batteries is not entirely straightforward, as the information is largely based on manufacturers’ specifications and plans and is therefore subject to uncertainties.
In detail, the technology differs considerably in some cases, but most manufacturers plan to use Li metal as the anode (e.g. QuantumScape [4]). The cathode material is essentially the same as for Li-ion batteries, although it should be noted that some solid electrolytes are not compatible with all cathode materials. Oxide, sulfide, or polymer-based materials can be used as electrolytes (More information on solid-state electrolytes can be found here), with polymer batteries being the closest to production-ready today.
Selection of the cells to be compared
Four configurations are compared: Two Li-ion cells and two solid-state batteries. For the two lithium-ion batteries, a graphite anode with 10% silicon admixture is assumed as the anode in each case. In laboratory tests, this has already doubled the capacity compared to pure graphite anodes [5], although it cannot be assumed that these values will be achieved in practice. NMC811 is selected as the cathode for high-energy applications and LFP for long-life applications.
Promising material combinations for solid-state chemistry have already been described in the literature [6], which is why we refer to them here for comparison.
Li metal is considered as the anode in both cases. For the first solid-state cell, NMC811 and a sulfide electrolyte are used. With this electrolyte, operation at room temperature is basically possible and decent charge rates can also be achieved, but an intermediate layer between electrolyte and anode is probably necessary to prevent parasitic reactions [6].
The second solid-state cell is based on a cell concept pursued by Blue Solutions [7] and has a polymer separator in addition to a Li metal anode. Although this is already very close to series production (used e.g. in Mercedes eCitaro [8]), it has the disadvantage that operation at ambient temperature is not possible and the battery must be heated. Due to the low stability window of the separator, LFP is used as the cathode, which is associated with a lower energy density [6].
Results of the comparison

Figure 1: Advantages and disadvantages of solid-state batteries compared to Li-ion batteries. Comparison of the development status as expected for 2028, Own illustration.
Figure 1 shows a network diagram comparing the cells in terms of their safety, power, energy density, lifetime and expected costs. The strengths and weaknesses of the cells differ considerably and it can be seen that there is no cell variant that can convince in all categories.
In terms of energy density, the solid-state battery with NMC cathode and sulfide electrolyte performs best. The literature describes that the energy density could be up to 25% higher compared to today’s Li-ion batteries [6]. Due to the Li metal anode, the LFP solid-state battery achieves values that are only reached with NMC cathodes in Li-ion cells, and even a further increase in energy density is conceivable in the long term at cell level. However, heating is necessary due to the polymer electrolyte.
The power picture is ambivalent. Due to the poor ionic conductivity of polymer electrolytes, the LFP solid-state battery cannot be expected to achieve high performance and therefore performs worse than LFP Li ion cells, which can deliver comparatively high power. Li-metal anodes generally tend to deposit more lithium and associated dendrites at high currents, so that high performance will not be possible in the medium term and solid-state batteries do not perform better overall than NMC Li-ion cells.
Cell safety tends to be better with solid-state batteries than with Li-ion batteries because a higher temperature window can be used. Exothermic reactions leading to thermal runaway only occur at higher temperatures, resulting in generally improved safety. However, solid-state batteries with Li anode are much more prone to dendrite formation, which makes the occurrence of internal short circuits more likely. LFP as a cathode material is much more robust than NMC in this regard because the PO4 compound is chemically more stable than that of CoO2 and releases oxygen only slowly [9]. The LFP solid-state battery therefore performs best in terms of safety.
The lifetime of solid-state batteries is limited primarily by the mechanical stresses caused by volume changes during charging and discharging. Resulting consequential damages are unstable interface connections between the electrodes and the electrolyte. While liquid electrolyte is expected to age faster than solid electrolyte, solid-state batteries are not expected to last longer than Li-ion cells due to the stability issues of solid-state batteries. (More on this in the article here). LFP as cathode favors the lifetime of the cell and already more than 4000 cycles could be achieved in studies for LFP solid-state batteries[6].
From a cost perspective, the NMC solid-state battery in particular falls behind the others, especially because commercialization has not yet progressed as far for sulfide-based electrolytes. The increased demand for lithium for the metal anodes of the solid-state batteries is also expected to drive the price. Therefore, established material combinations with only a few scarce raw materials are expected to be the cheapest.
Conclusion
In many comparisons, today’s Li battery is compared with a future solid-state battery, as it will be on the market in a few years. This comparison is misleading because the development of Li-ion batteries is progressing and significantly improved properties are expected with new innovations such as the addition of silicon to the anode.
If we compare how both types of electrolyte – liquid and solid – will develop in the second half of the 2020s, the picture is very ambivalent. On the basis of today’s data, the conclusion is that none of the technologies can convince comprehensively. Due to scaling effects, the Li-ion battery will remain cheaper than solid-state batteries for a long time to come. In terms of safety and service life as well as energy density, the mechanical stress caused by changes in volume during charging and discharging means that the solid-state battery is not convincing and it is not yet foreseeable that the mechanical problems can be completely solved by the time it is ready for series production. Only in terms of energy density is it clear that solid-state batteries will outperform lithium-ion batteries and achieve new record values. However, this is probably not enough to displace lithium-ion batteries.
Sources
[1] Wood Mackenzie: Will semi-solid battery technology render solid-state batteries redundant?, https://www.woodmac.com/news/opinion/will-semi-solid-battery-technology-render-solid-state-batteries-redundant/
[2] IDTechEX: The State of the Li-Ion Industry, November 2022, Online Webinar, The State of the Li-ion Industry : IDTechEx Webinar
[3] Haregewoin, A., Wotango, A. et al.: Electrolyte additives for Lithium ion battery electrodes: progress and perspectives, 2017 Energy & Environmental Science
[4] Quantumscape: Delivering on the promise of solid-state technology, 2023, https://www.quantumscape.com/technology
[5] Moyassari, E., Streck, L. et al.: Impact of Silicon Content within Silicon-Graphite Anodes on Performance and Li Concentration Profiles of Li-Ion Cells using Neutron Depth Profiling, 2021, Journal of The Electrochemical Society
[6] Fraunhofer Institute for Systems and Innovation Research ISI: Solid-State Battery Roadmap 2035+, Karlsruhe, 2022
[7] Blue-Solutions: Battery Technology, 2023, https://www.blue-solutions.com/en/battery-technology/)
[8] Mercedes Benz: eCitaro, Battery Technology, 2023, https://www.mercedes-benz-bus.com/de_DE/models/ecitaro/technology/battery-technology.html
[9] HardingEnergy: Lithium Iron Phosphat, Harding Energy | Lithium Ion batteries | Lithium Polymer | Lithium Iron Phosphate, Stand: 01/2023