Korean Silicon Lithium Battery Anode Research Progress

Researchers from POSTECH and Sogang University developed a functional polymeric binder for stable, high-capacity anode material that could increase the current EV range at least 10-fold over current graphite anode electric car battery range. There is already commercial use of electric cars with 3-8% silicon anode by weight with out 10-30% range increases. There are about 2000 research papers every month on the topic of improvement of silicon for anodes. There is quite bit of lab work with silicon usage in the 30-40% weight range. There needs to be a process with more silicon that can be rapidly productionized and scaled for use in billions of battery cells and millions of electric vehicles.

Korean researchers developed charged polymeric binder for a high-capacity anode material that is both stable and reliable, offering a capacity that is 10 times or higher than that of conventional graphite anodes. This breakthrough was achieved by replacing graphite with Si anode combined with layering-charged polymers while maintaining stability and reliability. The research results were published as the Front Cover Article in Advanced Functional Materials.

If there is more silicon in a battery anode then it has more energy. However, silicon expands and can reduce the number of times the anode can be charged and with too much expansion it can break the battery entirely. In 2023, Tesla has reportedly added up to 5 percent silicon in its batteries’ anodes.

Benefits and the Major Challenge of Silicon in Anodes
The reaction mechanism of silicon with lithium is via intermetallic alloying. This reaction allows silicon to provide almost ten times higher capacity (3600 mAh/g) than graphite (372 mAh/g) with the same weight. Using more silicon-based anodes has improved energy density by at least by 30 % of actual values.

Anode manufacturers are introducing silicon into the electrodes but at rather low weight percentages of around 3 to 8 %, due to the complexities presented by silicon during the cycling of the battery: silicon particles undergo enormous volume changes, i.e., up to 300 % of volume expansion (while in the case of graphite it is 13 %).

CIC energiGUNE has published scientific results with high content silicon anodes (30 – 40 weight percentage of silicon at electrode level).

1. 2016, Applied Materials and Interfaces. Silicon-Reduced Graphene Oxide Self-Standing Composites Suitable as Binder-Free Anodes for Lithium-Ion Batteries.
Self-standing silicon-based anodes (silicon-reduced graphene oxide, 40 wt.% of Si) were fabricated and explored, showing great cycling stability (750 mAh/g at 0.05 A/g).

2. Molecules Journal (2020) Towards a High-Power Si@graphite Anode for Lithium Ion Batteries through a Wet Ball Milling Process. A simple, low-cost and easily scalable approach to prepare silicon-graphite composite electrodes (30 wt. % of Si) which exhibited stable capacity values of 850 mAh/g at a rate of 0.25 A/g and outstanding capacity of 770 mAh/g at a rate of 5 A/g, and the importance of the electrode microstructure and design was highlighted.

There are companies like Amprius and OneD trying to use nanowires. Nanowires are a good alternative to conventional flat and round morphologies since volume changes are almost negligible because nanowires leave room for expansion.

Researchers are using CMC for binders that can handle the expansion of more silicon.

There have been about 13000 published articles related to silicon-based anodes in the first half of 2023.

South Korea Polymer Silicon Anode 2023 Research

Research to date has focused solely on chemical crosslinking and hydrogen bonding. Chemical crosslinking involves covalent bonding between binder molecules, making them solid but has a fatal flaw: once broken, the bonds cannot be restored. Hydrogen bonding is a reversible secondary bonding between molecules based on electronegativity differences, but its strength (10-65 kJ/mol) is relatively weak.

The new polymer developed by the research team not only utilizes hydrogen bonding but also takes advantage of Coulombic forces (attraction between positive and negative charges). These forces have a strength of 250 kJ/mol, much higher than that for hydrogen bonding, yet they are reversible, making it easy to control volumetric expansion. The surface of high-capacity anode materials is mostly negatively charged, and the layering-charged polymers are arrayed alternately with positive and negative charges to effectively bind with the anode. Furthermore, the team introduced polyethylene glycol to regulate the physical properties and facilitate Li-ion diffusion, resulting in the thick high-capacity electrode and maximum energy density found in Li-ion batteries.

Advanced Functional Materials – Layering Charged Polymers Enable Highly Integrated High-Capacity Battery Anodes (2023)

Abstract
High-capacity anode materials are promising candidates for increasing the energy density of lithium (Li)-ion batteries due to their high theoretical capacities. However, a rapid capacity fading due to the huge volume changes during charge-discharge cycles limits practical applications. Herein, a layering-charged polymeric binder is introduced that can effectively integrate high-capacity anodes using a strong yet reversible Coulomb interaction and enriched hydrogen bonding. The charged polymeric binder builds a dynamically charge-directed network on the active materials with high versatility and efficiently dissipates the electrode stress with its excellent mechanical properties. In addition, poly(ethylene glycol) (PEG) moieties of the charged binder offer a fast Li-ion conduction pathway that can form an ultra-thick silicon oxide (SiOx)-based electrode (≈10.2 mAh cm−2) without compromising the reversible specific capacity and promote effective charge interaction as a mechanical modulator. Such an unprecedented charge-directed binder provides insights into the rational design of a binder for high-capacity anodes.