The Effect of Volume Change on the Accessible Capacities of Porous Silicon-Graphite Composite Anodes

Abstract

Silicon-graphite (Si/C) composite anodes are used to increase total anode capacity while maintaining a tolerable degree of active material volume expansion. However, increasing the Si/C ratio does not directly lead to an increase in the accessible capacity because excessive volume expansion can lead to unacceptable cell pressure or electrode porosity. To predict the accessible capacity as a function of Si/C ratio, we integrated mechanical behavior for individual cell components into our previous battery model that couples mechanical and electrochemical phenomena and then simulated a full charge of a pouch cell with foam packing. The simulations were used to determine the anode accessible capacity as a function of Si/C ratio, based on practical pressure and porosity design limitations. The resulting predictions illustrate the tradeoff between the capacity gained by increasing the Si/C ratio and the accessible capacity lost based on the pressures that build up in the cell due to the interconnected mechanical and electrochemical phenomena. For a given set of cell and pack design requirements, battery designers can use these types of simulations as a tool to maximize accessible capacity of an operating cell by selecting appropriate cell/pack materials and identifying optimal Si/C ratios.

Accounting for Non-Ideal, Lithiation-Based Active Material Volume Change in Mechano-Electrochemical Pouch Cell Simulation

“…The fundamental governing equations and construction of the coupled mechano-electrochemical model used in this study has been described in previous work. [20][21][22][23] During charging and discharging, Li + ions move from the cathode to the anode and from the anode to the cathode, respectively. The lithiation and de-lithiation of the anode and cathode lead to active material volume change.…”

“…Recently, our group incorporated measured mechanical behavior for the individual cell components and cell packing to simulate realistic electrode-scale and cell-scale mechanical responses. 23 This MSM was used to show how varying the Si/C ratio in the composite anode would affect cell pressure generation and electrode porosity during cell operation.…”

BIAN-Based Porous Organic Polymer as a High-Performance Anode for Lithium-Ion Batteries

“…9−13 This mechanism leads to a huge volume expansion in lithiation, followed by contraction during delithiation. 14,15 This causes the loss of conductivity and unstable solid electrolyte interphase (SEI) generation. Hence, much effort is being directed toward optimizing the morphology of the active material 16−20 and toward developing polymeric materials, 3,21−24 which can negotiate volume change.…”

“…reported the utilization of Si-based composites as anodic materials in lithium-ion batteries . However, the charge storage in these systems is based on an alloy/de-alloy mechanism. − This mechanism leads to a huge volume expansion in lithiation, followed by contraction during delithiation. , This causes the loss of conductivity and unstable solid electrolyte interphase (SEI) generation. Hence, much effort is being directed toward optimizing the morphology of the active material − and toward developing polymeric materials, ,− which can negotiate volume change.…”

Probing component contributions and internal polarization in silicon-graphite composite anode for lithium-ion batteries with an electrochemical-mechanical model

“…[14,15] As for the modeling of Si-Gr composite anodes, some recent models focus on the mechanical behavior of composite anodes. [16][17][18] However, very few theoretical studies examine the (de)lithiation competition between Si and Gr and polarization of the cell with Si-Gr composite anodes. [19] In this work, we present an electrochemical-mechanical model to investigate the electrochemical and stress behavior of the LIBs with Si-Gr anodes by analyzing the individual electrochemical behavior of Si and Gr.…”