In-situ acoustic emission study of Si-based electrodes for Li-ion batteries

Self Cite

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...

Section: Resultsmentioning

confidence: 99%

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

Tranchot

Idrissi

Thivel

et al. 2016

Self Cite

“…Experimental characterization of fracture evolution within Si active particles during lithiation-delithiation cycles, have been reported in several research articles. 65,66 The essence of acoustic emission based techniques lie behind the fact that during microcrack formation, some strain energy gets released. It propagates through the media as a stress wave and reaches the surface.…”

Section: Resultsmentioning

confidence: 99%

“…A similar acoustic emission based experimental procedure have been adopted by Trancot et al to characterize the evolution of mechanical degradation within a 2 μm sized Si active particle over 10 lithiation-delithiation cycles. 66 In the present study, similar lithiation-delithiation simulations have been conducted on a spherical active particle of initial diameter 2 μm over 10 cycles. Figure 11 demonstrates the comparison between evolution of mechanical degradation extracted from simulations (black solid line) and the experimentally observed cumulative damage (blue circles).…”

Section: Resultsmentioning

confidence: 99%

Mechano-Electrochemical Stochastics in High-Capacity Electrodes for Energy Storage

Barai

Mukherjee

2016

High-capacity anode materials (such as, silicon) are of critical importance for lithium-ion batteries aimed at achieving longer drive range for electric vehicles. Large lithium retention in these alloying materials is, however, accompanied by high volume expansion, which results in severe mechanical degradation and capacity decay. The inherently coupled mechano-electrochemical stochastics is elucidated in this work. A stochastic computational methodology has been developed to capture the large deformation and mechanical degradation in high-capacity anode materials. Lithiation and delithiation in such active particles follow a two-phase diffusive interface formation and propagation. Mechano-electrochemical interactions lead to different tensile forces acting on the active particle that may lead to microcrack formation. In this study, we have demonstrated that: (a) concentration gradient induced stress at the two-phase interface does not lead to severe mechanical degradation; and (b) large volume expansion induced tensile force at the particle surface actually gives rise to multiple spanning crack formation and further propagation during delithiation. Anode materials with higher partial molar volume of the lithiated phase can lead to enhanced mechanical degradation. Functionally graded materials, with reduced elastic modulus near the surface, hold potential for significant reduction in crack formation. Lithium-ion batteries (LIBs) are poised to play a major role in the advancement toward wide-spread vehicle electrification.1-3 Significant effort is being invested to make use of lithium ion chemistry in commercial aircrafts (see 4,5 ) as well as large-scale grid energy storage systems (see 6,7 ). Increasing the specific energy of both cathode (see 8,9 ) and anode (see 10,11 ) electrode active material will effectively result in enhanced energy density of the LIB. Commercial batteries use lithium cobalt oxide (LiCoO 2 ) or nickel-manganese-cobalt (LiNi 1/3 Mn 1/3 Co 1/3 O 2 ) as the cathode material, which shows around 170mAh/g as the effective specific energy.12 Graphite is used regularly as anode active material within commercial batteries, which shows a maximum of 372mAh/g specific capacity. 12Next generation lithium ion batteries are supposed to use high capacity cathode as well as anode materials.11 Layered-layered composite cathode structures, represented as xLi 2 MnO 3 · (1-x)LiMO 2 (M = Mn, Ni, Co), has received attention due to high rechargeable capacity of 250mAh/g when cycled between 4.6 V and 2.0 V (see [13][14][15] ). Gas generation due to oxygen release is one of the major modes of degradation in these composite cathode materials. These high-capacity layered composite cathodes do not experience severe volume expansion during lithiation process. 16 High capacity anode materials can show almost ten times higher theoretical specific energy than graphite (such as, silicon (Si), tin (Sn) and germanium (Ge)) (see [17][18][19][20] ). The theoretical capacity of silicon is 4200mAh/g and the same for tin is 994...

“…Several acoustic emission based experiments have been conducted to understand how fracture evolves within solid active particles. 48,49,62 In all the three research articles, it has been reported that mechanical degradation initiates at the first lithiation-delithiation cycle. Maximum amount of microcrack evolves in the first one or two cycles.…”

Section: Methodsmentioning

confidence: 99%

“…48,62 Hence, an experimental counterpart of the maximum amount of mechanical degradation parameter (A max ) is the maximum cumulative strain energy release observed from acoustic emission experiments. Saturation in the strain energy release has been reported in several experimental articles, 48,49,62 which is equivalent to the saturation in evolution of microcrack density observed by the authors. 50 Most of the reduced order models are derived from systematic reduction of governing differential equations.…”

Section: Methodsmentioning

confidence: 99%

Reduced Order Modeling of Mechanical Degradation Induced Performance Decay in Lithium-Ion Battery Porous Electrodes

Barai

Smith

Chen

et al. 2015

A one-dimensional computational framework is developed that can solve for the evolution of voltage and current in a lithium-ion battery electrode under different operating conditions. A reduced order model is specifically constructed to predict the growth of mechanical degradation within the active particles of the carbon anode as a function of particle size and C-rate. Using an effective diffusivity relation, the impact of microcracks on the diffusivity of the active particles has been captured. Reduction in capacity due to formation of microcracks within the negative electrode under different operating conditions (constant current discharge and constant current constant voltage charge) has been investigated. At the beginning of constant current discharge, mechanical damage to electrode particles predominantly occurs near the separator. As the reaction front shifts, mechanical damage spreads across the thickness of the negative electrode and becomes relatively uniform under multiple discharge/charge cycles. Mechanical degradation under different drive cycle conditions has been explored. It is observed that electrodes with larger particle sizes are prone to capacity fade due to microcrack formation. Under drive cycle conditions, small particles close to the separator and large particles close to the current collector can help in reducing the capacity fade due to mechanical degradation. Due to their high energy and power density, lithium-ion batteries (LIBs) are being used extensively in the electrification of the automotive industry through the development of electric and hybrid electric vehicles (EVs and HEVs).1-3 Several mechanisms exist that can cause a reduction in the capacity of LIBs and subsequent loss of life. [4][5][6][7] Growth of a solid electrolyte interface (SEI) layer on the carbon active particles of the anode is the major reason behind the loss of cyclable lithium ions. [8][9][10] Lithium plating at low temperatures also results in loss of lithium and subsequent capacity fade.11 Delamination of the current collector from the electrode due to gas evolution in the electrolyte can significantly increase the internal resistance of the lithium-ion cell. 12 Crack propagation, rupture, and isolation of portions of active particles can also cause loss of active sites where lithium atoms can intercalate, resulting in effective capacity fade. 13 In the past two to three decades, capacity fade due to the formation of SEI 8,10,[14][15][16][17] and lithium plating 18,19 have been investigated thoroughly. On the other hand, resistance growth and capacity fade due to delamination and site loss have not been explored extensively. In the recent past, some research initiatives have focused on characterizing the generation of diffusion-induced stress within the active particles. 20 A computational methodology was developed to capture the formation of cracks based on the material heterogeneity of the anode active particles. 21 In the present article, the authors have developed a comprehensive reduced order model (RO...