South Korea develops innovative battery technology to help extend electric vehicles' range

When a battery is fully charged, an electronic device will typically display 100% capacity. However, because lithium-ion batteries experience permanent losses during the first charge during the stabilization (formation) phase of battery production, 100% capacity typically represents only 70% to 90% of the theoretical energy density that the battery can store. If lithium-ion batteries could be prevented from experiencing losses during the first charge, the range of electric vehicles (EVs) and the usability of smartphones could be greatly increased.

Research parameters (Image source: KIST)

According to foreign media reports, in order to overcome this problem, the Korea Institute of Science and Technology (KIST) formed a joint team with the Energy Storage Research Center, Energy Materials Research Center, and Hydrogen Fuel Cell Research Center to develop an electrode pretreatment solution that can minimize the initial lithium-ion battery loss in the graphite silicon oxide (SiOx) composite anode. After immersion in the solution, the lithium ion loss of the anode made of 50% graphite silicon oxide is almost negligible, allowing the entire battery to achieve a near-ideal energy density.

Although most commercial lithium batteries use graphite anodes, graphite silicon oxide has a capacity 5 to 10 times that of graphite and is therefore considered the next generation anode material. However, graphite silicon oxide consumes three times as much active lithium as graphite. Therefore, composite electrodes made by mixing graphite and graphite silicon oxide have been recognized as the next generation of practical anodes. However, when the content of graphite silicon oxide is high, the capacity of the graphite-graphite silicon oxide composite electrode will increase accordingly, and at the same time, the initial lithium loss will also increase. Therefore, the proportion of graphite silicon oxide in the graphite-graphite silicon oxide composite electrode should be limited to 15%, because if it is increased to 50%, the initial lithium loss will reach 40%.

To achieve both high capacity and high initial efficiency, scientists have proposed various pre-lithiation methods, including doping additional lithium into the anode in advance. KIST researchers developed a process to immerse the electrode in a special solution to reduce the consumption of lithium by graphite silicon oxide. The team then applied the process to graphite-graphite silicon oxide composites, which have great commercial potential.

The research team found that due to the multifunctional intercalation function of graphite, the pretreatment solution previously developed could cause solution molecules with lithium ions to be accidentally inserted into graphite. The insertion of such large solution molecules would cause structural damage to the graphite-graphite silicon oxide composite electrode. To prevent electrode failure, the researchers developed a new solution that uses a weak solvent to reduce the interaction between the solvent and lithium ions. This solution is able to selectively insert lithium ions into the active material, ensuring a stable supply of additional lithium to the graphite-graphite silicon oxide composite electrode.

The graphite-graphite silicon oxide electrode was immersed in the solution developed by the research team for about 1 minute, and even when the graphite silicon oxide content reached 50%, the initial lithium consumption was completely avoided. Therefore, when the initial efficiency of the electrode reached nearly 100%, it meant that the lithium loss (≤ 1%) was negligible during the first charge. The electrode capacity made by this process was 2.6 times higher than that of traditional graphite anodes. At the same time, after 250 charge and discharge cycles, 87.3% of the initial capacity was maintained.

Minah Lee of KIST said: "Based on the research results, compared with the conventional materials, in which the content of graphite silicon oxide in the graphite-graphite silicon oxide composite anode is only allowed to be 15%, the new process can increase the content to more than 50%, thereby enabling the production of lithium-ion batteries with larger capacity and improving the driving range of future electric vehicles. The technology is also safe and suitable for mass production, so it is expected to be commercialized."