So, what has semi-solid got that solid-state hasn’t?
A recent report – The elusive holy grail: the challenge for solid-state batteries – delved into the future of battery tech. Visit the store to access it in full, or read on for an overview of key themes.
Scale is a key issue for solid-state batteries
The foremost reason solid-state hasn’t moved from the pilot plant to the gigafactory is a matter of scale. The fundamental enabling component is the solid electrolyte, which replaces a liquid version in current, traditional lithium-ion battery (LIB) batteries. However, the solid electrolyte still needs to achieve what is easy for liquids – to infiltrate all empty spaces in a cell in order to boost performance and promote longer cycle life.
The electrolyte area in one EV is roughly the area of three tennis courts. So it’s near impossible to construct a solid electrolyte that keeps as high a contact area with electrodes as a liquid can – without using very precise and slow manufacturing techniques. For this reason, solid-state batteries have failed to surpass fingernail sizes in the semiconductor industry, where batteries are constructed in vacuums and on an atom-by-atom scale.
If next-generation technology is to meet the demand for better and safer EVs, a high-scale manufacturing technique is needed.
Semi-solid battery technology offers a compromise
While solid-state developers have been struggling with this issue since the turn of the century, or longer, some have accepted a compromise technology – semi-solid.
By combining both solid and liquid electrolyte components, the issues of low contact areas and slow manufacturing techniques are overcome. But semi-solid is no golden goose. The liquid electrolyte adds more weight and volume to the cell, meaning the improvement in cell energy, and therefore EV range, is restricted – though still an improvement on current cells.
Two major Chinese automakers, NIO and Dongfeng Motor, have planted their flags in the semi-solid camp. They have each announced production of EVs next year using the tech, supplied by WeLion and Ganfeng Lithium, respectively. While the cell energy is less than what full solid-state may promise, the compromise technology is a leap forward that can be manufactured at scale – possibly leaving solid-state redundant.
Lithium supply is a challenge for both battery technologies
There could be a spanner in the works for both technologies. Their energy-boosting performance comes from the use of a lithium metal anode that replaces bulky and charge-limiting graphite.
The luxury vehicle segment alone could account for roughly 100 GWh of demand by 2030 – resulting in an extra 81 kt lithium carbonate equivalent (LCE) demand. That equates to 7% of available lithium supply that year.
Not only is this an extra strain on an already tightening market, but lithium metal foils are high-performance materials with stringent purity requirements. So much so that the global production capacity is currently just 12.8 kt LCE, less than a sixth of the capacity needed.
Ultimately, the progress of either technology may be hindered by the increasingly clear signs of insufficient lithium supply to the market, or by a lack of infrastructure in the production of high-requirement, specialist lithium anode materials.