Study of the Binder Influence on Expansion/Contraction Behavior of Silicon Alloy Negative Electrodes for Lithium-Ion Batteries

Abstract

In lithium-ion batteries, Si-based materials such as silicon alloys are regarded as a promising alternative to graphite negative electrode to achieve higher energy. Unfortunately, they often suffer from a large volume change that can result in poor cycle life. We monitored the electrode expansion/contraction that occurs during lithiation/delithiation in real time by electrochemical dilatometry. Volume changes of Si alloy-based electrode with three different polymer binders have been compared. Electrode manufactured with lithiated polyacrylic acid (LiPAA) exhibited the greatest expansion but also demonstrated the highest reversibility as well as the best cycling performance. Ex situ SEM imaging along with dilatometer measurements revealed that electrode porosity after contraction (delithiation) increases compared to that after precedent expansion (lithiation), which can buffer volume expansion at the subsequent cycle. Proof-of-concept in situ optical microscopy (IOM) experiments were carried out with the best performing LiPAA electrode. The results demonstrated that LiPAA electrode in the IOM cell expanded much less than the same electrode in the dilatometer cell. This implies that internal pressure existing in a lithium-ion cell has a great impact on total electrode expansion.

A Practical Guide for Using Electrochemical Dilatometry as Operando Tool in Battery and Supercapacitor Research

“…Different cathode materials (layered oxides, [9b,10] graphite [anion intercalation], [8c,8f] as well as anode materials [graphite, [8e,8j,9a,11] transition metal oxides, [8h,12] alloy‐based materials] [ 13 ] ) have been investigated with this method. In addition, many studies were done on silicon‐based materials [8a,8m,8n,9e,9n,14] as their large volume expansion is a known issue. Different methods to reduce this volume change were therefore explored, including different binder materials, [8m,14a,14g,14j,15] covering the electrodes with a thin film, [14b,14c] choosing different slurry pH values for the preparation, [14e] using different conductive additives, [14f] combining silicon with other elements, [8n,14p] and fabricating specialized nanostructures [14l] .…”

“…In addition, many studies were done on silicon‐based materials [8a,8m,8n,9e,9n,14] as their large volume expansion is a known issue. Different methods to reduce this volume change were therefore explored, including different binder materials, [8m,14a,14g,14j,15] covering the electrodes with a thin film, [14b,14c] choosing different slurry pH values for the preparation, [14e] using different conductive additives, [14f] combining silicon with other elements, [8n,14p] and fabricating specialized nanostructures [14l] . Different full‐cell configurations (graphite/ lithium nickel manganese cobalt oxides [NMC], [8e,9g,9l,16] graphite/ lithium cobalt oxide [LCO], [9c,9d,9j,9k,17] graphite/ LiMn 2 O 4 , [17b] lithium–titanate–oxide/NMC, [ 18 ] silicon–graphene/NMC, [9h] graphite‐blended Si/LCO, [9k] graphite‐blended Si/C/LCO, [9n] and graphite‐blended SiN(P)/NMC [9m] ) have been also studied using ECD.…”

“…Data from refs. [8a,8c,8e,8f,8h,8j,8m,8n,9c,10‐14,14j,14l‐r,15,20a‐d,20f‐k,22] (assignment of the different references to the materials can be found in Table S1 and S2, Supporting Information).…”

“…While this appears simple at first, different values may be obtained depending on the initial state of the electrode. The dry and pristine electrode, [8a,9b] the electrode after soaking in electrolyte, [14a] the electrode film excluding the current collector, [8n,9h,14e,14r,22h] or the thickness after the equilibration time [8f,20h] have been used as reference point h 0 . There is no clear right or wrong for determining h 0 as it depends on the experiment which method most suitable.…”

“…In supercapacitors, a correlation between the orientation of the ions and the shape of the thickness change was found [27b] . In addition, variations in the slopes can give information on the buffering ability of an electrode [14e] …”