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Interplay between electrochemical reactions and mechanical responses in silicon-graphite anodes and its impact on degradation.

ABSTRACT: Durability of high-energy throughput batteries is a prerequisite for electric vehicles to penetrate the market. Despite remarkable progresses in silicon anodes with high energy densities, rapid capacity fading of full cells with silicon-graphite anodes limits their use. In this work, we unveil degradation mechanisms such as Li⁺ crosstalk between silicon and graphite, consequent Li⁺ accumulation in silicon, and capacity depression of graphite due to silicon expansion. The active material properties, i.e. silicon particle size and graphite hardness, are then modified based on these results to reduce Li⁺ accumulation in silicon and the subsequent degradation of the active materials in the anode. Finally, the cycling performance is tailored by designing electrodes to regulate Li⁺ crosstalk. The resultant full cell with an areal capacity of 6 mAh cm^-2 has a cycle life of >750 cycles the volumetric energy density of 800 Wh L^-1 in a commercial cell format.

SUBMITTER: Moon J

PROVIDER: S-EPMC8113583 | biostudies-literature | 2021 May

REPOSITORIES: biostudies-literature

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Interplay between electrochemical reactions and mechanical responses in silicon-graphite anodes and its impact on degradation.

Moon Junhyuk J Lee Heung Chan HC Jung Heechul H Wakita Shinya S Cho Sungnim S Yoon Jaegu J Lee Joowook J Ueda Atsushi A Choi Bokkyu B Lee Sihyung S Ito Kimihiko K Kubo Yoshimi Y Lim Alan Christian AC Seo Jeong Gil JG Yoo Jungho J Lee Seungyeon S Ham Yongnam Y Baek Woonjoong W Ryu Young-Gyoon YG Han In Taek IT

Nature communications 20210511 1

Durability of high-energy throughput batteries is a prerequisite for electric vehicles to penetrate the market. Despite remarkable progresses in silicon anodes with high energy densities, rapid capacity fading of full cells with silicon-graphite anodes limits their use. In this work, we unveil degradation mechanisms such as Li<sup>+</sup> crosstalk between silicon and graphite, consequent Li<sup>+</sup> accumulation in silicon, and capacity depression of graphite due to silicon expansion. The ac ...[more]

PMID: 33976126

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Project description:Silicon is a promising next-generation anode to increase energy density over commercial graphite anodes, but calendar life remains problematic. In this work, scanning electrochemical microscopy was used to track the site-specific reactivity of a silicon thin film surface over time to determine if undesirable Faradaic reactions were occurring at the formed solid electrolyte interphase (SEI) during calendar aging in four case scenarios: formation between 1.5 V and 100 mV with subsequent rest starting at (1) 1.5 V and (2) 100 mV and formation between 0.75 V and 100 mV with subsequent rest starting at (3) 0.75 V and (4) 100 mV. In all cases, the electrical passivation of silicon decreased with increasing time and potential relative to Li/Li+ over a 3 day period. Along with the decrease in passivation, the homogeneity of passivation over a 500 μm2 area decreased with time. Despite some local "hot spots" of reactivity, the areal uniformity of passivation suggests global SEI failure (e.g., SEI dissolution) rather than localized (e.g., cracking) failure. The silicon delithiated to 1.5 V vs Li/Li+ was less passivated than the lithiated silicon (at the beginning of rest, the forward rate constants, kf, for ferrocene redox were 7.19 × 10-5 and 3.17 × 10-7 m/s, respectively) and was also found to be more reactive than the pristine silicon surface (kf of 5 × 10-5 m/s). This reactivity was likely the result of SEI oxidation. When the cell was only delithiated up to 0.75 V versus Li/Li+, the surface was still passivating (kf of 6.11 × 10-6 m/s), but still less so than the lithiated surface (kf of 3.03 × 10-9 m/s). This indicates that the potential of the anode should be kept at or below ∼0.75 V vs Li/Li+ to prevent decreasing SEI passivation. This information will help with tuning the voltage windows for prelithiation in Si half cells and the operating voltage of Si full cells to optimize calendar life. The results provided should encourage the research community to investigate chemical, rather than mechanical, modes of failure during calendar aging and to stop using the typical convention of 1.5 V as a cutoff potential for cycling Si in half cells.

Dataset Information

Interplay between electrochemical reactions and mechanical responses in silicon-graphite anodes and its impact on degradation.

Publications

Interplay between electrochemical reactions and mechanical responses in silicon-graphite anodes and its impact on degradation.

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