We simulated cold press fabrication and intercalation damage in a sulfide All-Solid-State Battery (ASSB) electrode using the Discrete Element Method. We developed a new cohesive hybrid-particulate model that both can simulate particle consolidation during fabrication and material failure during intercalation expansion. In this way, the effect of the fabrication conditions on the mechanical degradation of the electrode can be simulated. The high pressure in the cold press fabrication cause plastic deformation and build-up of cohesive contacts between the particles, consisting of Si active material (AM) and sulfide solid electrolyte (SE), resulting in densification of the electrode. During charging, when AM expands during lithiation, the AM-SE contact area increases but the effective SE conductivity decreases. When the expansion is small, the contact area and conductivity may recover to their original value. However, large expansion may cause plastic deformation and cracking that cause permanent reduction of both contact area and SE conductivity. This type of mechanical degradation was significantly less for electrodes fabricated at higher pressures. This model can become a valuable tool to improve the durability and performance of future ASSBs.
In order to increase energy density and enhance safety, all-solid-sate lithium-ion batteries have been developed as a storage battery for electric vehicle (EV). Further performance improvement of all-solid-sate lithium-ion batteries requires optimization of the electrode structure. In this paper, we constructed a phase interface model focusing on the microstructure of the porous electrode, and examined the reaction of the electrode layer structure.
Recently, all-solid-state-lithium-ion batteries have attracted attention as next-generation batteries serving as driving sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, it is required to have more power density and more energy density. In order to develop the performance of batteries, High-capacity negative active material (AM) such as Si have been developed, but their use is not easy due to severe expansion during charging and discharging [1]. Although materials with reduced expansion and contraction have been developed [2], it is unclear how much expansion of the AM is allowed in the first place and how much it affects the porous electrode structure. Also, since the performance of batteries depend not only on the material characteristics but also on its electrode structure, it is important to design an optimum electrode structure. Therefore, chasing the state in electrode layer using the numerical computation is a critical measure for the comprehension of phenomenon in the cell. However, in the relatively micro-scale system such as the electrode layer, a slight difference in structure affects the battery performance. However, usual simulations demand the reactive interface area and the tortuosity factor which critically affect the cell performance by reasonableness or approximation, as it might overlook the phenomenon from minute structure of electrode layer. Therefore, our laboratory has devised a multi-network model as a method that directly reflects the transport characteristics in the particle-packed structure [3]. In this study, we apply it to an all-solid-state battery and examine the effect of various structural factors on the expansion and contraction of the AM. This simulation first located AM particles randomly in three-dimensional space. The AM particles are all spherical and overlap is not allowed. Next, assuming the space except active material particles as solid electrolyte (SE) phase and located imaginary spheres with greatest diameter at positions fixed by 4 AM particles or more, which memorize electrolyte information such as ion electric potential at the position. After constructing electrode structure, the AM network and SE network were built as shown in Figure 1 The electronic conduction was calculated in AM network, as the ionic conduction calculated with SE network, while the electrode reaction occurring at interface between AM and SE. Finally, by applying this model to a galvanostatic discharge simulation based on the porous electrode theory [4], the state inside electrode layer was obtained with iterative computation by taking the mass balance and electron balance of each AM particles and SE particles. The structural change in the electrode layer due to the expansion and contraction of the AM was based on the previous research of this laboratory [5], and the discrete element method (DEM) was incorporated into the stress analysis. DEM is a method of calculating a force acting in a normal direction and a tangential direction between particles, assuming a spring representing elasticity and a dashpot representing viscous damping between particles in contact with each other. Using this, the interparticle stress in the electrode layer was calculated, and a dynamic change accompanying expansion and contraction of the AM was considered. With this model, it is possible to examine the effects of various structural factors and the optimal structural design in consideration of the expansion and contraction of the AM, and to provide guidelines for higher power density. Acknowledgment This research was supported by Grants-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices” MEXT, Japan FY2019-2023. Reference [1] X. Su et al., Adv. Energy Mater., 4, 1300882 (2014). [2] X. Zhang et al., Electrochemistry, 84 (6), 420 (2016). [3] K. Lin et al., ECS Transaction, 80(10), 251–258 (2017). [4] G. M. Goldin et al, Electrochimica Acta, 64 , 118-129 (2012). [5] K. Ishikawa et al, the 56th Battery Symposium in Japan, 3E16 (2015). Figure 1
Recently, all-solid-state lithium-ion batteries (ASSLiB) has emerged as one of the most promising candidates for next-generation power sources for electric vehicles (EVs) and energy storage. The main reason is the introduction of non-flammable solid electrolyte (SE) which substantially reduces the risk of battery fires. However, more research is needed in order to improve the durability and the overall performance. High charge capacity active material (AM) such as Si have been developed but their high expansion during charging and discharging reduces the durability. 1 During charge, AM in the cathode will absorb Lithium by intercalation and expand. A reverse contraction process occurs in the anode. This is known as Vegards expansion/contraction and cause buildup of high stresses, so called intercalation induced stresses. Although materials with less expansion/contraction have been developed, it is unclear how much expansion/contraction the materials in AM and SE can tolerate. Previous studies that model intercalation induced stress can be found in the literature. Most of the research is focused on the intercalation induced stresses either inside the AM or inside SE material. In the study of Bucci et al., 2 the stress in the SE due to Vegards expansion of AM was modelled by the finite element method (FEM) and the location of cracks could be predicted. However, according to Sun et al., 3 the critical region of failure is not within AM and SE but at the interface. Moreover, in FEM it is difficult to resolve the grained boundaries at the interfaces and the continuity assumption may not be valid as there are often void spaces between SE particles. These issues can be solved by modelling AM and SE as particles as in the Discrete Element Methods (DEM). In this study we perform DEM simulations and utilize the multisphere method for the AM particles. In the multisphere method, non-spherical particles are represented as a cluster of spherical sub-particles as illustrated in Figure 1 (a). We assume elliptical shapes which is in agreement with TEM image of graphite AM. In the DEM solver, the particle motion is determined from the forces acting on each particle. The elastic contact force between two particles with radii Ri and Rj is calculated by the Herzian contact law: F elastic = 4/3∙E eff δ 3/2 R eff 1/2 (1) where R eff = RiRj /(Ri + Rj ) is the effective radius and E eff is the effective elastic modulus given by 1/E eff = (1-ν i 2)/E i +(1-ν j 2)/E j (2) where E i and E j are the Young modulus of elasticity of the particles. In the DEM solver, collision damping force and the tangential forces due to static and kinetic friction are also calculated. The motion and rotation of each particle was calculated from the sum of forces and torques acting on the particles. A series of DEM simulations were conducted. Different aspect ratios of the elliptical shapes were generated and the relationship between the aspect ratio and circularity agreed well with the experimental results. A gravity driven packing simulation was conducted followed by a press simulation at 500 MPa and a release simulation to stack pressure at 25 MPa. In order to solve for the intercalation induced stresses, expansion of AM particle was calculated by gradually increasing the particle radius. The results of the spatial distribution of the stresses of the SE material is shown in Figure 2 in the case of a volume expansion of 10%. During cold pressing of ASSLiB electrode, the contact force is not perfectly elastic but plasticity effects of SE plays a role large role and is an important design parameter 4. In cold pressing applications the normal force is often modeled as follows 5 F normal = min(F elastic , F plastic ) (3) where F plastic is the plastic force. A model is currently under development that can simulate the effect of plasticity on stress and damage during cold pressing and intercalation. The model can aid in the development and selection of favorable of materials for ASSLiB electrode. This research was supported by Grants-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices” MEXT, Japan FY2019-2023. References M. N. Obrovac, L. Christensen, D. B. Le, and J. R. Dahn, J. Electrochem. Soc., 154, A849 (2007). G. Bucci, T. Swamy, Y.-M. Chiang, and W. C. Carter, ArXiv170300113 Cond-Mat (2017) http://arxiv.org/abs/1703.00113. C. Sun, J. Liu, Y. Gong, D. P. Wilkinson, and J. Zhang, Nano Energy, 33, 363–386 (2017). K. Nagao et al., Solid State Ion., 308, 68–76 (2017). C. L. Martin, D. Bouvard, and S. Shima, J. Mech. Phys. Solids, 51, 667–693 (2003). Figure 1
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.