Impact of the Slurry pH on the Expansion/Contraction Behavior of Silicon/Carbon/Carboxymethylcellulose Electrodes for Li-Ion Batteries

Abstract

Electrochemical dilatometry experiments were performed on silicon/carbon/carboxymethylcellulose (Si/C/CMC) composite electrodes prepared with pH7 and buffered pH3 slurries. It was shown that the pH3 electrode better accommodates the severe volume change of the micrometric Si particles, inducing a much better capacity retention with cycling (70% after 10 cycles compared to only 6% for the pH7 electrode). During the first discharge (lithiation), a maximum electrode thickness expansion of ∼170% was observed for the pH3 electrode compared to ∼330% for the pH7 electrode. A lower irreversible expansion was also observed at the end of the 1 st cycle (∼50% compared to ∼180% for the pH7 electrode). It was explained by the fact that the pH3 of the slurry, which is known to favor the formation covalent bonds between the Si particles and the CMC chains, greatly improves the cohesive strength of the electrode as supported by the higher hardness and elastic modulus of the pH3 electrode. When the discharge capacity was limited to 1200 mAh g −1 , a progressive and irreversible swelling of the pH3 electrode was observed upon prolonged cycling, which was attributed to the accumulation of solid electrolyte interface (SEI) products. Silicon is a very attractive active material for Li-ion battery anodes due to its ∼10 times higher gravimetric capacity and ∼3 times higher volumetric capacity than conventional graphite anode (i.e., 3579 mAh g −1 and 2190 mAh cm −3 for Li 15 Si 4 compared to 372 mAh g −1 and 719 mAh cm −3 for LiC 6 ). However, obtaining commercially viable Sibased anodes is very challenging due to the large volume expansion of Si during its lithiation (∼280% from Si to Li 15 Si 4 ).1 This leads to the fracture and rearrangement of the Si particles, inducing the rupture of the electrical network in the composite electrode. As a result, a rapid capacity decay with cycling is observed.2 The large Si volume change also induces an instability of the solid electrolyte interface (SEI), which continuously grows with cycling, decreasing the coulombic efficiency (CE) and increasing the electrode impedance.3 To address these issues, numerous strategies have been investigated for several years as reviewed in Refs. 4-8 with a few significant successes in the improvement of the cycle life of Si-based electrodes (>1000 cycles, at least in half-cell).9-15 Actually, further work is still required to tackle the issue of SEI stability and to obtain low-cost Si-based electrodes with practical relevant surface, gravimetric and volumetric capacities.Considering that the volume change of Si-based electrodes largely contributes to their degradation, monitoring their expansion and contraction with cycling is highly relevant to evaluate the impact of the composite electrode formulation and morphology, and cycling conditions on this process. For this purpose, a simple and efficient method consists of integrating a non-contact gap sensor 16 or a contact displacement transducer 17 to the electrochemical cell, which permits a measurement of any ver...

Silicon Nanoparticles with a Polymer-Derived Carbon Shell for Improved Lithium-Ion Batteries: Investigation into Volume Expansion, Gas Evolution, and Particle Fracture

“…This is unfavorable, especially when considering that the volume expansion of Si particles is accommodated to some extent by the electrode’s porosity. 29…”

Real‐Time Dilation Observation of Si‐Alloy Electrode Using Thermally Treated Poly (Amide‐Imide) as a Binder for Lithium Ion Battery

“…[22][23][24][25][26][27][28] Among the various binder materials to be considered for Si-based high capacity anode materials, poly (amide-imide) (PAI) shows some promising behavior as a binder for Si-based electrodes because of its high mechanical strength by secondary interaction from polyimide and hydrogen bonding from amide group in polyamide. [22][23][24][25][26][27][28] Among the various binder materials to be considered for Si-based high capacity anode materials, poly (amide-imide) (PAI) shows some promising behavior as a binder for Si-based electrodes because of its high mechanical strength by secondary interaction from polyimide and hydrogen bonding from amide group in polyamide.…”

“…Yang et al reported that simple heat treatment can further improve the cycle performance of Si-alloy electrode adopting PAI binder. To the best of our knowledge, although in situ dilatometric studies on the Si-based electrode using other binder materials such as carboxymethylcellulose (CMC), 27 Polyimide (PI), 25 PVDF 26 are reported, there are few reports on in-situ dilation monitoring of Si-based electrode employing PAI binder. 28 One can reasonably expect that thermally treated PAI binder, which have strong binding force, can suppress the volume expansion and reduce electrical contact loss of electrode.…”

“…To utilize a proper binder material that can suppress the volume changes of a Si electrode during cycling would be an important method to improve the stable capacity retention of Si‐based anode materials . Among the various binder materials to be considered for Si‐based high capacity anode materials, poly (amide‐imide) (PAI) shows some promising behavior as a binder for Si‐based electrodes because of its high mechanical strength by secondary interaction from polyimide and hydrogen bonding from amide group in polyamide .…”

“…Even though ex‐situ SEM observation on the cross‐section of the cycled Si electrode revealed the volume suppression due to the improved mechanical properties of PAI binder, direct and more detailed analysis on the volume variations of Si electrode is necessary to understand the effect of mechanical strength on the electrochemical performance of Si‐based high capacity anode material during lithiation and delithiation. To the best of our knowledge, although in situ dilatometric studies on the Si‐based electrode using other binder materials such as carboxymethylcellulose (CMC), Polyimide (PI), and PVDF are reported, there are few reports on in‐situ dilation monitoring of Si‐based electrode employing PAI binder. In this study, in‐situ electrochemical dilatometer was employed to observe the dynamic dilation behaviors of Si‐alloy electrodes adopting PAI with respect to temperature for heat treatment.…”