Better Knowing the Carbon Particle Network Structure in Electrode Slurry for Enhanced Lithium-Ion Battery Performance
Authors: Jeevan Kumar Padarti , Fukamizu Kaito , Suzuki Hisao , Hirai Shigeto , Matsuda Takeshi , Ohno Tomoya 
Published: December 2024

1. Introduction
Achieving higher capacity lithium-ion batteries requires a delicate balance between a high amount of active materials and a minimum amount of conductive additives within electrode slurries. These slurries, dispersed in a non-aqueous polymeric suspension, rely on homogeneous dispersibility of active materials and conductive additives[1]. However, challenges arise from the tendency of carbon black (average size <100 nm, falling under the colloidal regime) to aggregate, compromising battery efficiency. Achieving well-dispersed carbon conductive additives and a stable, well-connected three-dimensional percolated network structure within the slurry with a minimal amount of carbon additive is a significant challenge. To address this challenge, our research focuses on optimizing the carbon percolation network within electrode slurries utilizing the fundamentals of electrochemical impedance spectroscopy (EIS). Our aim is to evaluate particle dispersibility within the slurry, providing valuable insights into structural changes under both steady-state and applied shear forces (various flow conditions). This innovative approach offers a promising avenue for streamlining manufacturing processes and advancing lithium-ion battery technology towards greater efficiency and performance. EIS enables detailed analysis of resistance/constant phase elements (CPE) values based on differences in the frequency response of the electric double layer, offering insight into various sizes of particle single/aggregated/agglomerated/ network structures within the slurry[2].
Furthermore, the non-destructive nature of electrochemical impedance spectroscopy facilitates in-situ measurements using a flow cell to investigate structural changes under applied shear forces and aging effects under steady-state conditions. Preliminary investigations into the correlation between impedance and particle dispersibility pave the way for future evaluations under both steady-state and shear forces (various flow conditions), offering a promising avenue for optimizing electrode slurry manufacturing processes. We also investigated the dispersibility of carbon particles in Li-ion conducting electrolyte media to differentiate the effect of dispersibility. This comprehensive approach not only highlights the critical role of carbon particle network structures within electrode slurries but also presents a meaningful impact in the field of lithium-ion battery technology.
2. Experimental
The experimental approach involves increasing the content of acetylene black (AB) in non-aqueous binder suspensions as well as Li-ion conducting liquid from 0.3 wt.% to 10 wt.%. Electronic conductivity is evaluated using a specially designed cell for electrochemical impedance spectroscopy (EIS) under steady state and flow conditions. Analysis of slurry intermediate states with varying AB solid content provides insights into structural changes and better knowing the primary/aggregates and agglomerated states of AB, including network formation. Rheological properties of the slurry are also analyzed to establish the relationship between AB particle dispersion and solid content. Additionally, particle sedimentation is assessed in relation to aging. To validate findings, the slurry is freeze-dried between microslides for morphological observations and rheology analysis.
3. Results and Discussion
As depicted in Figure 1, at low carbon concentrations, the electrochemical response exhibits characteristics akin to an electrochemical capacitor, mainly influenced by the resistance of the polymeric binder. However, at higher carbon concentrations, a well-defined electronic percolating network forms, leading to an impedance response shift from a linear pattern to a semicircular shape. The mixing process of electrode particles induces shear stress, potentially fragmenting the network structure. Moreover, particle sedimentation may contribute to the formation of aggregates and agglomerates. Hence, understanding and optimizing the carbon percolation network are crucial for ensuring effective electronic conduction and promoting homogeneity, even under varying flow conditions. Investigation of slurry impedance degradation with increasing AB content via EIS, supported by morphological observations and rheology analysis, yields valuable insights into enhancing lithium-ion battery performance. The study delves into comprehending the electron conduction network under steady state and various slurry flow rates, along with the rheological properties of electrode slurries. The impedance measurement results reveal a correlation between impedance and particle dispersibility, with the formation of a three-dimensional network structure at higher AB concentrations. Structural changes over time in the slurry with a three-dimensional network structure indicate further development, underscoring the significance of optimizing carbon percolation networks for enhanced electrochemical performance in lithium-ion battery electrodes.
4. Conclusion
This study highlights the critical role of carbon conductive particles in lithium-ion battery electrode slurries. Optimizing their dispersion and network structure is pivotal for achieving high conductivity and enhancing electrochemical performance. These findings hold significant potential for advancing lithium-ion battery technology towards greater efficiency and performance and also stand as a best slurry quality check when shifting to new electrode material combinations.

References

(1) J. K. Padarti, S. Hirai, H. Sakagami, T. Matsuda, T. Ohno, J. Ceram. Soc. Japan,
130, 832 (2022).
(2) J. K. Padarti, Ľ. Gabániová, S. Hirai, T. Matsuda, H. Suzuki, T. Ohno, 第59回粉体に関する討論会, December (2022).

Figure 1