(Invited) Mitigation of Electrode Swelling of Pure Si Nano-Flake Anode for Advanced Lithium-Ion Batteries

Abstract

The poor cyclability of pure Si electrodes is attributed to crack formation and pulverization of Si active material due to a large volume expansion and contraction during charging and discharging, respectively. It is thus important to suppress the physical stress induced by the large volume changes to improve the cyclability of Si electrodes. We designed a Si powder with a flake shape (Si LeafPowder®, Si-LP, OIKE & Co., LTD.) with 100 nm in thickness and 3-5 mm in lateral dimension, and have reported that Si-LP electrodes have a high initial discharge capacity (ca. 2,500 mAh g-1) and good cycleability (Fig. 1) [1]. Another serious problem of Si anode is a swelling of the electrode owing to irreversible microstructural changes of Si nano-flakes upon cycling (Fig. 2) [2]. The Si-LP sheets in a composite electrode were substantially deformed during alloying/de-alloying cycling and formed the multi-folded layered structure on repeated cycling. Furthermore, many voids, which could accommodate volume changes of Si, were formed on repeated cycling. The multi-folded layered structure with many voids enabled the stable battery operation of the Si-LP electrodes. Though good cycleability is obtained, the observed electrode swelling during cycling (Fig. 3) is not affordable for practical use. In this talk, we present some mitigation methods developed for suppression of electrode swelling of Si-LP anode and Si thin film anode, including the effects of additives (VC, FEC in Fig.4) [2], the effects of particle size, the effects of oxide content [3], the effects of pre-film formation [4], the effects of artificial SEI film [5], etc. This research was supported by Japan Science and Technology Agency (JST) ALCA-SPRING and Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number 16H04649.