Fast Ion Migration Research Articles

Bimetal Fluorides with Adjustable Vacancy Concentration Reinforcing Ion Transport in Poly(ethylene oxide) Electrolyte.

The poor ambient ionic transport properties of poly(ethylene oxide) (PEO)-based SPEs can be greatly improved through filler introduction. Metal fluorides are effective in promoting the dissociation of lithium salts via the establishment of the Li-F bond. However, too strong Li-F interaction would impair the fast migration of lithium ions. Herein, magnesium aluminum fluoride (MAF) fillers are developed. Experimental and simulation results reveal that the Li-F bond strength could be readily altered by changing fluorine vacancy (VF) concentration in the MAF, and lithium salt anions can also be well immobilized, which realizes a balance between the dissociation degree of lithium salts and fast transport of lithium ions. Consequently, the Li symmetric cells cycle stably for more than 1400 h at 0.1 mA cm-2 with a LiF/Li3N-rich solid electrolyte interphase (SEI). The SPE exhibits a high ionic conductivity (0.5 mS cm-1) and large lithium-ion transference number (0.4), as well as high mechanical strength owing to the hydrogen bonding between MAF and PEO. The corresponding Li//LiFePO4 cells deliver a high discharge capacity of 160.1 mAh g-1 at 1 C and excellent cycling stability with 100.2 mAh g-1 retaining after 1000 cycles. The as-assembled pouch cells show excellent electrochemical stability even at rigorous conditions, demonstrating high safety and practicability.

Reduced graphene oxide-supported Na3V2(PO4)3/C cathode material synthesized by sol-gel method to improve electrochemical performances of sodium-ion batteries

Na-ion batteries are potential alternative to Li-ion batteries due to their low cost and abundance of sodium source. And Na3V2(PO4)3 is regarded as the most promising cathode material because of their high capacity and larger interstitial channels for fast Na ion migration. However, the disadvantage of low conductivity suppresses its practical applications. To increase electrochemical properties of the cathode, reduced graphene oxide-supported Na3V2(PO4)3/C (NVP/C-G) composite has been prepared, in which the graphene is used to accelerate movement of the electronics and Na ions. XRD characterizations show that the synthesized material is well corresponding to NASICON structure, and SEM image show that the graphene sheets are uniformly dispersed on surface of the composite. The initial capacity of the material is up to 103.5 mAh g−1 at 0.1 C, and 92.3 % and 92.1 % of capacities are maintained with discharge ratios of 0.5 C and 2 C over 500 cycles, proving a much better cycling stability compared with the Na3V2(PO4)3/C (NVP/C) particles. The enhanced discharge capacities and retention rate of the NVP/C-G could be ascribed to the tight contact between NVP/C and RGO sheets, which is beneficial to fast electron transport and better intercalation/deintercalation of Na+ through the nanoparticles. Therefore, the synthesized NVP/C-G displays highly potential for practical use in sodium-ion batteries.

Designing Heterodiatomic Carbon Hydrangea Superstructures via Machine Learning-Regulated Solvent-Precursor Interactions for Superior Zinc Storage.

Carbon superstructures with exquisite morphologies and functionalities show appealing prospects in energy realms, but the systematic tailoring of their microstructures remains a perplexing topic. Here, hydrangea-shaped heterodiatomic carbon superstructures (CHS) are designed using a solution phase manufacturing route, wherein machine learning workflow is applied to screen precursor-matched solvent for optimizing solvent-precursor interaction. Based on the established solubility parameter model and molecular growth kinetics simulation, ethanol as the optimal solvent stimulates thermodynamic solubilization and growth of polymeric intermediates to evoke CHS. Featured with surface-active motifs and consecutive charge transfer paths, CHS allows high accessibility of zincophilic sites and fast ion migration with low energy barriers. A anion-cation hybrid charge storage mechanism of CHS cathode is disclosed, which entails physical alternate uptake of Zn2+/CF3SO3 - ions at electroactive sites and chemical bipedal redox of Zn2+ ions with carbonyl/pyridine motifs. Such a beneficial electrochemistry contributes to all-round improvement in Zn-ion storage, involving excellent capacities (231 mAh g-1 at 0.5 A g-1; 132 mAh g-1 at 50 A g-1), high energy density (152Wh kg-1), and long-lasting cyclability (100000 cycles). This work expands the design versatilities of superstructure materials and will accelerate experimental procedures during carbon manufacturing through machine learning in the future.

Porous nickel–cobalt phosphate with oxygen-rich vacancies in situ grown on dopamine-modified cellulose textiles as self-supporting high mass loadings supercapacitor electrode

Transition-metal phosphates/phosphides showcase significant promise for energy-related applications because of their high theoretical electrochemical characteristics. However, sluggish electro/ion transfer rates and kinetically unfavorable reaction sites hinder their application at high mass loading. Herein, a self-supporting electrode based on transition-metal phosphates was successfully fabricated via a one-step electrodeposition process. The nanosheet structure of transition-metal phosphates, formed by interconnecting nanoparticles, effectively mitigates the impact of stress and achieves a high mass-loading (21 mg cm−2) of the electrode. Additionally, the oxygen vacancy-rich and porous nanostructure of transition-metal phosphates endows the as-prepared electrodes with a significantly increased conductivity and fast ion migration rate for enhancing electrochemical kinetics. Consequently, the as-fabricated transition-metal phosphate electrode displays the highest areal specific capacity of 39.2F cm−2. Furthermore, the asymmetric supercapacitor achieves a maximum energy density of 0.79 mWh cm−2 and a high capacity retention of 93.0 % for 10000 cycles under 60 mA cm−2. This work provides an ideal strategy for fabricating flexible electrodes with high mass loading and synthesizing transition-metal phosphate electrodes rich in oxygen vacancies.

O-Targeted Carbon Hybrid Orbital Conversion to Produce sp2-Rich Closed Pores for Sodium-Storage Hard Carbon.

Biomass-based hard carbon has the advantages of a balanced cost and electrochemical performance, making it the most promising anode material for sodium-ion batteries. However, due to the structural limitations of biomass (such as macropores and impurities), it still faces the problems of low specific capacity and initial Coulombic efficiency (ICE). Herein, an integrated strategy of biomass liquefaction and oxidation treatment is proposed to fabricate hard carbon with low ash content and sp2-rich closed pores. Specifically, liquefaction treatment can break through the inherent constraints of biomass, while oxidation treatment with O-targeted effect can directionally convert C─C/C─O bonds into C═O/O═C─O bonds, which would promote the formation of closed pores and the rearrangement into sp2-carbon within the graphene layer. Moreover, it is well demonstrated that the hard carbon interface rich in sp2 hybridization can induce the generation of an inorganic-rich solid electrolyte interface, contributing to fast ion migration and excellent interfacial stability. As a result, the optimized hard carbon with maximum closed pore volume and sp2/sp3 ratio can exhibit a high capacity of 347.3mAhg-1 at 20mAg-1 with the ICE of 90.5%, and a capacity of 110.4mAhg-1 at 5.0Ag-1 after 10000 cycles.

Electrodeposition of polyaniline on reduced graphene oxide/cotton yarn with tunable electrochemical performance for flexible textile supercapacitors

Graphene/cotton fibers show significant promise in wearable energy storage due to their low cost, porous structure, and exceptional integration ability into wearable systems. However, the eco-unfriendly reductants and standalone electric double-layer capacitor hindered their application. Herein, a green and rapid hydrothermal-electrodeposition method was proposed to fabricate polyaniline (PANI) decorated reduced graphene oxide (rGO)/cotton yarns without using any chemical reductants and oxidants. The PANI/rGO/cotton (PRC) yarn exhibited porous conductive network, structural controllability, and mechanical flexibility. Additionally, the PRC yarn electrode delivers a fast electron transport and ion migration, synergistic energy storage contribution, and a controllable capacitance (up to 81.2 mF cm−1 at 0.2 mA cm−1). The assembled yarn supercapacitor shows a good capacitance (19.8 mF cm−1 at 0.08 mA cm−1), excellent energy-power density (2.7 μWh cm−1 at 40 μW cm−1), and great capacitance retention. This green fabrication of PRC yarns brings new insights into the development of wearable energy storage.

2D Halide Perovskites for High-Performance Resistive Switching Memory and Artificial Synapse Applications.

Metal halide perovskites (MHPs) are considered as promising candidates in the application of nonvolatile high-density, low-cost resistive switching (RS) memories and artificial synapses, resulting from their excellent electronic and optoelectronic properties including large light absorption coefficient, fast ion migration, long carrier diffusion length, low trap density, high defect tolerance. Among MHPs, 2D halide perovskites have exotic layered structure and great environment stability as compared with 3D counterparts. Herein, recent advances of 2D MHPs for the RS memories and artificial synapses realms are comprehensively summarized and discussed, as well as the layered structure properties and the related physical mechanisms are presented. Furthermore, the current issues and developing roadmap for the next-generation 2D MHPs RS memories and artificial synapse are elucidated.

Enabling fast diffusion/conversion kinetics by thiourea-induced wrinkled N, S co-doped functional MXene for lithium-sulfur battery

The long lifespan of high-energy density lithium-sulfur batteries (LSBs) is still hindered by severe polysulfide (PS) shuttling and sluggish sulfur reduction/evolution kinetics process. Herein, we report a facile preparation of thiourea-induced wrinkled nitrogen and sulfur co-doped functionalized MXene (NSMX) to modify the separator to enhance the ion diffusion and conversion kinetics for high-energy LSBs. The combination of theoretical calculations and experimental conclusions demonstrates that the introduction of N, S heteroatoms induces the shift of the d-band center in transition metal Ti towards the Fermi level and results in the robust bonding effect between N/S atoms and Li atom in PS, hence exhibiting admirable adsorption capability to PS and fast catalytic PS reversible conversion rate, which quickly deplete soluble high-order PS and expedites the depletion of the Li2S6 in high potential. The 2D wrinkled polar surface with excellent conductivity assures fast electron transfer and ion migration. Profiting from the enhancement of S utilization and the reduction of unfavorable accumulated Li2S6, the LSBs equipped with NSMX modified separators exhibit a high specific capacity of 1249 mAh g−1 at 0.2 C. At a high rate of 5 C, the LSBs also delivered an impressive reversible capacity of 600 mAh g−1. Moreover, a high capacity and stable cycling can be achieved even under the condition of high S load and lean electrolyte consumption.

Porous Carbon Cloth@CoSe2 as Kinetics‐Enhanced and High‐Loading Integrated Sulfur Host for Lithium–Sulfur Batteries

AbstractCarbon cloth (CC) possesses great potential as a sulfur host because of its excellent conductivity, flexibility, and easily modified free‐standing structure. However, the previous works do not take full advantage of CC except for the role of support and current collector. The smooth surface, small specific surface area, and poor binding force between coating materials and CC matrix are unfavorable for loading coating materials. The slow redox kinetics and low sulfur loading of sulfur cathodes still seriously restrict the development of Lithium–Sulfur (Li–S) batteries. Herein, the porous carbon cloth loading cobalt selenide (PCC@CoSe2) is constructed as an integrated sulfur host through a pore‐creating and selenylation strategy. The pore‐creating engineering greatly optimizes the 3D pore structure of CC to raise the sulfur and catalyst loading and provides enough space to accommodate the volume change of sulfur species. In addition, CoSe2 particles as nano‐catalyst units embedded in PCC can effectively adsorb‐catalyze polysulfides and improve the reaction kinetics. The resulting integrated sulfur cathode has realized the high‐efficiency polysulfide catalytic conversion and fast lithium ion migration, significantly enhancing redox kinetics and sulfur loading.

A Fluorinated Solid‐state‐electrolyte Interface Layer Guiding Fast Zinc‐ion Oriented Deposition in Aqueous Zinc‐ion Batteries

AbstractAqueous zinc ion batteries are gaining popularity due to their high energy density and environmental friendliness. However, random deposition of zinc ions on the anode and sluggish migration of zinc ions on the interface would lead to the growth of zinc dendrites and poor cycling performance. To address these challenges, we developed a fluorinated solid‐state‐electrolyte interface layer composed of Ca5(PO4)3F/Zn3(PO4)2 via an in situ ion exchange strategy to guide zinc‐ion oriented deposition and fast zinc ion migration on the anode during cycling. The introduction of Ca5(PO4)3F (FAP) can increase the nucleation sites of zinc ions and guide the oriented deposition of zinc ions along the (002) crystal plane, while the in situ formation of Zn3(PO4)2 during cycling can accelerate the migration of zinc ions. Benefited from our design, the assembled Zn//V2O5 ⋅ H2O batteries based on FAP‐protected Zn anode (FAP‐Zn) achieve a higher capacity retention of 84 % (220 mAh g−1) than that of bare‐Zn based batteries, which have a capacity retention of 23 % (97 mAh g−1) at 3.0 A g−1 after 800 cycles. This work provides a new solution for the rational design and development of the solid‐state electrolyte interface layer to achieve high‐performance zinc‐ion batteries.

A Fluorinated Solid-state-electrolyte Interface Layer Guiding Fast Zinc-ion Oriented Deposition in Aqueous Zinc-ion Batteries.

Aqueous zinc ion batteries are gaining popularity due to their high energy density and environmental friendliness. However, random deposition of zinc ions on the anode and sluggish migration of zinc ions on the interface would lead to the growth of zinc dendrites and poor cycling performance. To address these challenges, we developed a fluorinated solid-state-electrolyte interface layer composed of Ca5 (PO4 )3 F/Zn3 (PO4 )2 via an in situ ion exchange strategy to guide zinc-ion oriented deposition and fast zinc ion migration on the anode during cycling. The introduction of Ca5 (PO4 )3 F (FAP) can increase the nucleation sites of zinc ions and guide the oriented deposition of zinc ions along the (002) crystal plane, while the in situ formation of Zn3 (PO4 )2 during cycling can accelerate the migration of zinc ions. Benefited from our design, the assembled Zn//V2 O5 ⋅ H2 O batteries based on FAP-protected Zn anode (FAP-Zn) achieve a higher capacity retention of 84 % (220 mAh g-1 ) than that of bare-Zn based batteries, which have a capacity retention of 23 % (97 mAh g-1 ) at 3.0 A g-1 after 800 cycles. This work provides a new solution for the rational design and development of the solid-state electrolyte interface layer to achieve high-performance zinc-ion batteries.

Defect-induced electron rich nanodomains in CoSe0.5S1.5/GA realize fast ion migration kinetics as sodium-ion capacitor anode

Optimizing charge migration and alleviating volume expansion in anode materials are the key to improve the electrochemical performance for sodium-ion storage devices. Herein, a hierarchical porous conducting matrix confining defect-rich selenium doped cobalt dichalcogenide (CoSe0.5S1.5/GA) is constructed as a promising SICs anode based on the guidance of theoretical calculation analysis. The increased defect concentration significantly enhanced the disorder degree of the compound and presented electron aggregation around the S atoms, which effectively modulated the electronic structure, further enabling high rate and ultra-capacity sodium storage. Moreover, strong interfacial coupling could construct spatial constraint to alleviate volume expansion as well as maintain electrode integrity and stability. The CoSe0.5S1.5/GA electrode can deliver a high capacity of 310.1 mA h g−1 after 2000 cycles at 1 A g−1, and the CoSe0.5S1.5/GA//AC sodium ion capacitor can exhibit an outstanding energy density of 237.5 W h kg−1. A series of characterization and theoretical calculation convincingly reveal that the defect moieties can regulate the Na+ storage and diffusion kinetics, which prove that our defect manufacture coupling with space-confined strategy can provide deep insights into the development of high-performance Na+ storage devices.

Versatile potassium vanadium fluorophosphate (KVPO4F) composites as Dual-Function cathode and anode materials for Potassium-Ion hybrid capacitors

Potassium-based energy storage has emerged as a promising alternative for advanced energy storage systems, driven by the abundance of potassium, fast ion migration, and low standard electrode potential. Hybrid capacitors, which combine the desirable characteristics of batteries and supercapacitors, offer a compelling solution for efficient energy storage. In this study, we present the development of versatile composite materials, specifically potassium vanadium fluorophosphate (KVPO4F) composites, utilizing a sol–gel method. These composites enable tunable potassium storage and charge transport kinetics within regulated voltage windows, serving as both cathode and anode materials. The anode composite, composed of KVPO4F and hierarchical porous carbon (HPC), exhibited exceptional stability over 400 cycles within a low-voltage window. On the other hand, the cathode composite, consisting of battery-like KVPO4F and physisorption activated carbon (AC), demonstrated great potential as a cathode material, striking a balance between specific energy and cycle life within a regulated high-voltage window. By integrating KVPO4F/C as the anode and KVPO4F/AC as the cathode, we successfully created potassium-ion hybrid capacitors (PIHCs) that showcased an impressive capacity retention of 83% after 10,000 cycles within a high voltage window of 0.5–4.3 V. Furthermore, to explore the application of these materials in miniaturized energy storage, we fabricated potassium-ion micro hybrid capacitors (PIMHCs) with interdigitated electrodes. These devices exhibited a high areal energy density of 18.8 μWh cm−2 at a power density of 111.6 μW cm−2, indicating their potential for compact energy storage systems. The results of this study demonstrate the versatility and efficacy of the developed KVPO4F composite materials, highlighting their potential for future advancements in potassium-based energy storage technologies.

High performance of solid electrolyte endowed by SiO2 cross-linking agent towards lithium metal battery

A dual network solid polymer electrolyte is prepared, the cross-linked part is constructed using ring-opening polymerization reaction, in which SiO2 particles connect with polyethylene glycol diglycidyl ether (PEGDE) and polyetheramine (PEA) as cross-linking point. The introduction of SiO2 is conducive to reduce the crystallization of polymer matrix, improve the strength and promote the fast migration of Li ions. The abundant C-O segments in PEGDE and PEA are advantageous to the hopping behavior of Li ions and improve the ionic conductivity of electrolyte. Poly (vinylidenefluoride-hexaflouropropylene) (PVDF-HFP) is selected as linear part due to its robust mechanical behavior and outstanding electrochemical property. The obtained SiO2 functionalized PEGDE and PEA-PVDF-HFP solid polymer electrolyte (referred to as SGPP-ASPE) demonstrates excellent ionic conductivity of 2.4 × 10−4 S cm−1, high lithium-ion transference number of 0.54 and minor interfacial polarization of 0.09 V after 1000 h using Li//Li symmetrical cell. After assembling Li/LiFePO4 cell, a favorable cycling stability with the capacity retention of 93.8% after 100 cycles at 0.2 C is delivered. The reasonable design of advanced polymer electrolytes with dual network opens up a new path for the development of solid high-performance LMBs.

Biphasic high-entropy layered oxide as a stable and high-rate cathode for sodium-ion batteries

O3-phase layered oxides are promising cathode materials for sodium-ion batteries. However due to the strong Na+–O2- electrostatic attraction and the large size of Na ion, the O3 type cathodes suffer inferior rate capability and undesired phase transitions induced fast capacity fading. Herein, we propose a synergetic strategy of secondary phase (P2) and high-entropy to alleviate the aforementioned problems. Such a novel biphasic high-entropy (B-HE) layered cathode Na0.85Li0.05Ni0.25Cu0.025Mg0.025Fe0.05Al0.05Mn0.5Ti0.05O2 exhibits a specific capacity of 122 mAh g−1 at 0.2C, outstanding rate capacity of 81.8 mAh g−1 at 10C, and long-term cycling stability of ∼ 90% capacity retention after 1000 cycles at 10C. In situ XRD and electrochemical characterization demonstrate reversible phase transition of O3/P2 ↔ P3/P2 ↔ OP2/OP4, and the long-term existed P phase with fast Na ion migration paths. This biphasic high-entropy design strategy provides a promising road for advanced cathodes of Sodium-ion batteries.

Three-dimensional porous Na4MnV(PO4)3 constructed by Aspergillus niger biological template as a high performance cathode for sodium ion batteries

The sodium super ion conductor (NASICON) structure materials have attracted extensive attention because of its open three-dimensional crystal network framework and fast sodium ion migration rate. However, the poor electronic conductivity due to the presence of phosphate groups and the consequent high cost have been a barrier to commercialization. In this work, Na4MnV(PO4)3 (NMVP) with three-dimensional porous structure is synthesized in situ using Aspergillus niger as a biological template (noted as NMVP/ANDC). The cell wall of Aspergillus niger is rich in hydroxyl groups, which can adsorb metal ions well, so that NMVP particles can be synthesized on Aspergillus niger without stacking and agglomeration. NMVP grows along Aspergillus niger mycelium has a spongy-like three-dimensional porous network structure, which helps the contact between active materials and electrolyte, reduces the migration distance of sodium ions, and improves the conductivity of active materials. Therefore, NMVP/ANDC has good rate performance and cycle stability. It can provide 109 mAh g−1 at 0.5 C and 79.6% capacity retention after 3000 cycles at 5 C. The biological template method is proposed in this paper opens up a simple way for the preparation of other three-dimensional porous network structural materials.

Suppressing Ion Migration of Mixed‐Halide Perovskite Quantum Dots for High Efficiency Pure‐Red Light‐Emitting Diodes

AbstractPerovskite‐based light‐emitting diodes (PeLEDs) with a mixed halide composition can be used to obtain the “pure red” emission, i.e., in the 620–650 nm range, required for high‐definition displays. However, fast halide ion migration induces phase separation in these materials under electric fields, resulting in poor spectral stability and low efficiency. Herein, a method for producing mixed halide CsPbI3‐xBrx quantum dots (QDs) is reported in which ion migration is suppressed. The mixed halide composition is first achieved by anion exchange between CsPbI3 QDs and hydrobromic acid (HBr), during that the bromine ions efficiently passivate the iodine vacancies of the QDs. The original oleic acid ligands are then exchanged for 1‐dodecanethiol (1‐DT), which suppresses halide ion migration via the strong binding of the sulfhydryl group with the QD surface. PeLEDs based on these QDs exhibit a pure‐red electroluminescence (EL) peak at 637 nm, a maximum external quantum efficiency (EQE) of 21.8% with an average value of 20.4%, a peak luminance of 2653 cd m−2, and low EQE decease with increasing luminance. The EL spectrum of these devices is stable even at 6.7 V and they have an EQE half‐life of 70 min at an initial luminance of 150 cd m−2.

Multilevel resistive switching in stable all-inorganic n-i-p double perovskite memristor

Memristors are promising information storage devices for commercial applications because of their long endurance and low power consumption. Particularly, perovskite memristors have revealed excellent resistive switching (RS) properties owing to the fast ion migration and solution fabrication process. Here, an n-i-p type double perovskite memristor with "ITO/SnO2/Cs2AgBiBr6/NiOx/Ag" architecture was developed and demonstrated to reveal three resistance states because of the p-n junction electric field coupled with ion migration. The devices exhibited reliable filamentary with an on/off ratio exceeding 50. The RS characteristics remained unchanged after 1000s read and 300 switching cycles. The synaptic functions were examined through long-term depression and potentiation measurements. Significantly, the device still worked after one year to reveal long-term stability because of the all-inorganic layers. This work indicates a novel idea for designing a multistate memristor by utilizing the p-n junction unidirectional conductivity during the forward and reverse scanning.

Vacancy Engineering for High-Efficiency Nanofluidic Osmotic Energy Generation.

Two-dimensional (2D) nanofluidic membranes have shown great promise in harvesting osmotic energy from the salinity difference between seawater and fresh water. However, the output power densities are strongly hampered by insufficient membrane permselectivity. Herein, we demonstrate that vacancy engineering is an effective strategy to enhance the permselectivity of 2D nanofluidic membranes to achieve high-efficiency osmotic energy generation. Phosphorus vacancies were facilely created on NbOPO4 (NbP) nanosheets, which remarkably enlarged their negative surface charge. As verified by both experimental and theoretical investigations, the vacancy-introduced NbP (V-NbP) exhibited fast transmembrane ion migration and high ionic selectivity originating from the improved electrostatic affinity of cations. When applied in a natural river water|seawater osmotic power generator, the macroscopic-scale V-NbP membrane delivered a record-high power density of 10.7 W m-2, far exceeding the commercial benchmark of 5.0 W m-2. This work endows the remarkable potential of vacancy engineering for 2D materials in nanofluidic energy devices.

In Situ Observation of Photoinduced Halide Segregation in Mixed Halide Perovskite

Mixed–halide perovskites have emerged as a promising candidate for optoelectronics, due to their tunable optical properties. However, photoinduced phase segregation remains an obstacle for stable performance in solar cells. Here, we have conducted both bulk and nanoscale measurements to elucidate the mechanism of halide ion migration that leads to phase segregation. By utilizing Kelvin probe force microscopy (KPFM) under illumination, we have observed the time-evolution of ion migration to and from grain boundaries that agreed with bulk photoluminescence spectra of perovskites with a wide range of band gaps (1.67–1.88 eV), Cs0.15FA0.65MA0.20Pb(IxBr1–x)3 where x = 0.47–0.80. By visualizing the changes of band bending at grain boundaries, we deduce that halide segregation is dominantly caused by iodide ions, given faster ion migration in perovskite materials with a higher iodine content. Further, we verify that the changing rate of band bending at grain boundaries is consistent with the emerging rate of I-rich phase at grain boundaries, suggesting the influence of iodide ion migration toward grain boundaries on I-rich phase transition. This work will help provide insight for interpreting the mechanism of light-halide ion interactions.