Be it grid storage, computers, cell phones and especially electric vehicles, a safe, long-lasting, and energy-dense battery in a smaller form factor is what every company is looking for in selling their products today. ICE or internal combustion engine vehicles have dominated the last 100 years, but the next 100 years seems to be looking at a major change and while ICE auto's will be with us for some time, technology is going to change the way humans get around in the 21st century.
Let's start with a little background information on battery format. You have your Cylindrical size cells that is used by Tesla and a few other companies in the auto industry around the world. There is then the Prismatic cell format which has been used by Toshiba for their SCiB cells that are also being used by various auto companies and the last is Polymer a pouch size cell that is being used in the auto industry such as GM with their Ultium battery packs.
There are pros and cons to all formats depending on the company you talk too. Here we are not going to get into this area except to say that their is various weight with each type of format and of course the denser you can get the battery cell with long-life and safety while in a smaller format, the more flexible the design of an auto has.
The solid-state break through comes via a partnership of LG Energy Solutions and University of California Dan Diego.
Working together the engineers have created a new type of battery that combines two promising sub-fields into a single battery. The two areas are as follows, the solid state battery, being no liquid inside the battery and the anode which in traditional Lithium batteries is made of metallic lithium. Here the anode is made of 100% silicon. As such you have a solid state silicon battery cell. The research has shown that this design allows for a very safe, long-lasting and energy-dense cell. The applications of which can be applied to storage for the electrical grid to electric vehicles and so much more where battery technology is used.
From left to right in the picture above:
1) The all solid-state battery consists of a cathode composite layer, a sulfide solid electrolyte layer, and a carbon free micro-silicon anode.
2) Before charging, discrete micro-scale Silicon particles make up the energy dense anode. During battery charging, positive Lithium ions move from the cathode to the anode, and a stable 2D interface is formed.
3) As more Lithium ions move into the anode, it reacts with micro-Silicon to form interconnected Lithium-Silicon alloy (Li-Si) particles. The reaction continues to propagate throughout the electrode.
4) The reaction causes expansion and densification of the micro-Silicon particles, forming a dense Li-Si alloy electrode. The mechanical properties of the Li-Si alloy and the solid electrolyte have a crucial role in maintaining the integrity and contact along the 2D interfacial plane.
This battery technology was published in the Journal Science nanoengineers from University of California San Diego in collaboration with researchers at LG Energy Solutions made this breakthrough possible.
To quote the published report: The development of silicon anodes for lithium-ion batteries has been largely impeded by poor interfacial stability against liquid electrolytes. Here, we enabled the stable operation of a 99.9 weight % microsilicon anode by using the interface passivating properties of sulfide solid electrolytes. Bulk and surface characterization, and quantification of interfacial components, showed that such an approach eliminates continuous interfacial growth and irreversible lithium losses. Microsilicon full cells were assembled and found to achieve high areal current density, wide operating temperature range, and high areal loadings for the different cells. The promising performance can be attributed to both the desirable interfacial property between microsilicon and sulfide electrolytes and the distinctive chemomechanical behavior of the lithium-silicon alloy.
Silicon anode in traditional lithium batteries while safer have till now received much less attention due to the lower capacity these batteries hold. Yet solid-state has become a game changer with considerable increases in performance across a wide range of temperatures and excellent cycle life in full cell use.
What does one gain in going with this design? Currently a silicon anode in a solid-state battery is 10 times greater in energy density over a commercial lithium ion battery used in a BEV that is on the market. To quote the lead author on the paper, Darren H. S. Tan PhD in chemical engineering, "With this battery configuration, we are opening a new territory for solid-state batteries using alloy anodes such as silicon". Solid-state next generation batteries currently have had restrictions on charge rates and temperature during charging. The silicon anode overcomes these limitations, allows faster charging rates at room temperature while maintaining high energy density.
The laboratory testing delivered 500 charge and discharge cycles with 80% capacity retention at room temperature, which represents exciting progress for both the silicon anode and solid state battery technologies.
To understand why this is such an important breakthrough keep this in mind, silicon offers great storage capacity, 10 times greater than graphite. Lithium-ion batteries with silicon added to the anode mix increased energy density, but suffered from real-world performance issues; the number of times the battery can be charged and discharged while maintaining performance is not acceptable.
This problem is caused by the interaction of the silicon anodes and the liquid electrolytes it is paired with. This get complicated by the large volume of expansion of silicon particles during the charge and discharge cycle resulting in severe capacity losses over time.
Per the UC San Diego team, by eliminating the carbon and binders and going with an all-silicon anode using micro-silicon a much less processed and less expensive material over nano-silicon which has been used in the past they were able to reduce cost. They then addressed the root problem being the liquid electrolyte that causes instability. Here they used a sulfide-based electrolyte which showed this solid electrolyte to be extremely stable with the all-silicon anodes.
This creative out-of-the-box thinking has allowed them to have this breakthrough and will continue to support their research as they move forward on taking this to commercial productivity. This dual approach to battery design has removed the challenges that come with organic liquid electrolyte as they went with a solid electrolyte. It also allowed them to get ride of unwanted side reactions by removing the carbon on the anode with solid electrolyte, thus avoiding continuous capacity loss that typically occurs with liquid-base electrolytes.
This two-part move has allowed the researchers to reap the full benefits of low cost, dense or high energy and the properties of silicon being environmentally benign.
To quote LG Energy President and Chief Procurement officer Myung-hwan Kim; “With the latest finding, LG Energy Solution is much closer to realizing all-solid-state battery techniques, which would greatly diversify our battery product lineup.”
As the solid state battery race moves forward, LG will be bringing this to commercial market selling these batteries via their various partners such as a potential new battery design via GM's Ultium system