Cathode Interface Research Articles

Organosilica Nanodots Doped ZnO Cathode Interface Layer for Highly Efficient and Stable Inverted Polymer Solar Cells.

Interfacial engineering is essential to achieve optical efficiencies and facilitate the industrialization of organic solar cells (OSCs). By doping organosilica nanodots (OSiNDs) into zinc oxide (ZnO), we have developed a hybrid ZnO/OSiNDs (4 wt %) cathode interface layer (CIL) that significantly enhances the overall performance of inverted organic solar cells (i-OSCs). In the PM6/BTP-eC9 active layer system, i-OSC devices with a ZnO/OSiNDs (4 wt %) CIL exhibit a superior power conversion efficiency (PCE) of 17.49%, surpassing that of reference devices with a pure ZnO CIL (15.88%). The OSiNDs not only modulate the work function of ZnO, thereby facilitating the carrier transport between ZnO interface and active layer, but also enhance device stability. After exposure to 1200 min of 100 mW/cm2 illumination, including UV light, the devices retain 89.4% of their initial PCE, whereas devices based solely on ZnO retain only 57.7% under identical conditions. In this study, we present pioneering insights into the selection of environmentally friendly and cost-effective OSiNDs for modifying ZnO to create organic-inorganic hybrid coordination complexes as effective CILs.

Self-Reinforced Cathode Interface to Prolong the Cyclic Stability of Zn-MnO2 Batteries.

Rechargeable aqueous zinc-ion batteries (RAZIBs) are attracting increasing attention due to their advantages in safety, cost, and energy density. However, the choice of electrode binders when using aqueous electrolytes faces many constraints, as nontoxic and low-cost hydrophilic binders, such as sodium alginate (SA), can lead to electrode damage due to excessive swelling in aqueous solution. Here, by employing double-network hydrogel electrolytes formed by poly(vinyl alcohol) and alginate, the content and activity of water molecules at the electrode-electrolyte interface are reduced, and the mechanical stability of the electrode is reinforced, thereby affording reliable protection to the cathode bonded with SA. The quasi-solid-state interface formed between SA and the gel electrolyte provides stable electrode architecture and smooth ion transport, thus enabling Zn||MnO2 cells to exhibit excellent electrochemical cycling performance even when using hydrophilic binders.

Localized High-Concentration Electrolyte for All-Carbon Rechargeable Dual-Ion Batteries with Durable Interfacial Chemistry.

Lithium-based rechargeable dual-ion batteries (DIBs) based on graphite anode-cathode combinations have received much attention due to their high resource abundance and low cost. Currently, the practical realization of the batteries is hindered by easy oxidation of the electrolyte at the cathode interface, and solvent co-intercalation at the anode-electrolyte interface. Configuration of a "solvent-in-salt" electrolyte with a high concentration of Li salt is expected to stabilize the electrolyte chemistry versus both electrodes, yet inevitably reduces the mobility of the solvated working ions and increases the cost of the electrolyte. Herein, we propose to build a localized high-concentration electrolyte by adding hydrofluoroether as the diluent to reduce the salt content while improving the solvation structure, allowing more anions to enter the inner solvation sheath. The new electrolyte helps to form uniform and thin interfaces, with elevated contents of inorganic fluorides, on both electrodes, which effectively suppress electrolyte oxidation at the cathode and optimize electrolyte-electrode compatibility at the anode while facilitating charge transfer across the interface. Consequently, the DIBs with graphite as anode and cathode operate for 3000 cycles and retain a high-capacity retention of 95.7%, highlighting the importance of stable interfacial chemistry in boosting the electrochemical performance of DIBs.

Localized High‐Concentration Electrolyte for All‐Carbon Rechargeable Dual‐Ion Batteries with Durable Interfacial Chemistry

AbstractLithium‐based rechargeable dual‐ion batteries (DIBs) based on graphite anode‐cathode combinations have received much attention due to their high resource abundance and low cost. Currently, the practical realization of the batteries is hindered by easy oxidation of the electrolyte at the cathode interface, and solvent co‐intercalation at the anode‐electrolyte interface. Configuration of a “solvent‐in‐salt” electrolyte with a high concentration of Li salt is expected to stabilize the electrolyte chemistry versus both electrodes, yet inevitably reduces the mobility of the solvated working ions and increases the cost of the electrolyte. Herein, we propose to build a localized high‐concentration electrolyte by adding hydrofluoroether as the diluent to reduce the salt content while improving the solvation structure, allowing more anions to enter the inner solvation sheath. The new electrolyte helps to form uniform and thin interfaces, with elevated contents of inorganic fluorides, on both electrodes, which effectively suppress electrolyte oxidation at the cathode and optimize electrolyte‐electrode compatibility at the anode while facilitating charge transfer across the interface. Consequently, the DIBs with graphite as anode and cathode operate for 3000 cycles and retain a high‐capacity retention of 95.7 %, highlighting the importance of stable interfacial chemistry in boosting the electrochemical performance of DIBs.

Surface Reconstruction Reduces Internal Stress of Ni-Rich Cathode Particles.

High-voltage Ni-rich layered cathode materials are undoubtedly a powerful driving force for high-energy density lithium batteries. However, residual lithium impurities on the surface of Ni-rich materials can cause more severe side reactions under high-voltage, leading to rapid decay. There is still no reliable mechanistic explanation for this phenomenon. It has been detected that residual alkali on the cathode surface under high voltage can cause obvious side reactions. This side reaction will affect the capacity retention of the material and increase the internal stress of the particles. In addition, the surface reconstruction of Ni-rich cathodes is achieved through simple chemical reactions, turning waste into treasure. The newly generated Ti-based layer not only repairs the structure of the nickel-rich material but also optimizes the material from a dynamic perspective. Removing residual lithium components on the cathode surface effectively reduces the hydrolysis and self-catalytic side reactions of PF6 - at the electrolyte cathode interface and suppresses gas generation during cycling, promoting the application of the next generation of high-energy density Ni-rich layered cathode-based lithium batteries with high-voltage.

Research Progress on Solid-state Electrolyte Interface Problems in Lithium-ion Batteries

Nowadays, compared with traditional liquid batteries, solid-state batteries have the superiorities of higher energy density, power density and safety due to their solid electrolytes. However, a series of interfacial problems at solid-solid interface have always hindered the further development of solid-state batteries. Based on these problems, this paper firstly introduces the types of solid-state batteries and interface, secondly describes the mechanical failure principles of cathode interface and anode interface, and finally elaborates the corresponding modification strategies for cathode interface and anode interface. By adopting various improved measures for these interfacial problems, the progress of wider commercialization of solid-state batteries can be facilitated.

Engineering Molecule‐Designed In Situ Polymerization on Al‐Doped Molecular‐Sieve Framework Enables Robust Quasi‐Solid‐State Lithium Batteries

AbstractAchieving fast Li+ transport kinetics and stable electrode/electrolyte interfaces is of paramount importance, yet extremely challenging for the practical success of solid‐state lithium metal batteries, which requires the rational design of the structure and composition of solid‐state electrolytes. Herein, a composite quasi‐solid‐state electrolyte is fabricated through in situ polymerization of a molecule‐designed polymer chain within the functionalized molecular sieve framework (Al‐MCM41). In this design, the robust Brønsted/Lewis acid–base interactions between Al‐MCM41 and TFSI− facilitate the dissociation of lithium salt, leading to a Li+ transference number as high as 0.81. Meanwhile, the well‐ordered mesopores of Al‐MCM41 act as the “reservoir” of the polymer chain, creating continuous ionic migration pathways to offer an excellent Li+ conductivity of 1.09 × 10−3 S cm−1 at 30 °C. Furthermore, the polymer with fluorinated and nitrided functional groups guarantees a dual‐reinforced anode and cathode interface. Such an integrated electrolyte with simultaneous unimpeded Li+ transport and robust interfaces delivers extraordinary capacity retention of 84.6% over 600 cycles at 5 C when coupled with LiFePO4 cathode and remarkable reversible capacity of 129.0 mAh g−1 after 200 cycles with high‐voltage NCM622 cathode. This work provides a significant avenue for enhancing the practical feasibility of solid‐state lithium metal batteries.

Validating the Novel Electron Transport Layer with the Use of Experimentally Studied D18:Y6 Bulk Heterojunction Solar Cell

AbstractOrganic solar cells (OSC) are showing steady efficiency improvement due to the development in the materials synthesis, sophisticated characterization techniques, in‐depth understanding of materials and devices. In the recent years, bulk heterojunction OSC with a non‐fullerene acceptor /polymer acceptor shows significant enhancement in efficiency (≈19%). Efficiency of the polymer acceptor OSCs is much higher than the fullerene derivative‐based acceptors. In this work, OSC simulations are done using D18 donor and Y6 acceptor bulk heterojunction as a photoactive layer. As a first step, validity of the experimental results for ITO/PEDOT:PSS/D18:Y6/PDIN/Ag structure is done. To investigate efficiency, 2,8,15‐trifluoro‐3,9,14‐tris(heptylsulfonyl)diquinoxalino[2,3‐a:2′,3′‐c]phenazine (HATNASO2C7‐Cs) electron transport layer is validated in place of PDIN in the following device structure, ITO/PEDOT:PSS/D18:Y6/HATNASO2C7‐Cs/Ag. Energy level matching of the HATNASO2C7‐Cs is well aligned compared with PDIN at the cathode interface. Device simulation optimization are carried out for various photoactive layer, ETL and HTL condition. Highest efficiency of 20.99% is obtained for ITO/PEDOT:PSS/D18:Y6/HATNASO2C7‐Cs/Ag when the HATNASO2C7‐Cs thickness, bandgap, electron affinity, carrier mobility, and defect density is matched for ≈30 nm, ≈2.8 eV, ≈4.16 eV, ≈2 × 10−3 cm2 V−1 s−1, and 1014 cm−3 respectively. Obtained results are discussed in details and results will be helpful for preliminary understanding of the system.

Probing degradation at solid-state battery interfaces using machine-learning interatomic potential

Solid-state batteries featuring fast ion-conducting solid electrolytes are promising next-generation energy storage technologies, yet challenges remain for practical deployment due to electro-chemo-mechanical instabilities at solid-solid interfaces. These interfaces, which include homogeneous/internal interfaces such as grain boundaries (GBs) and heterogeneous/external interfaces between solid-electrolyte and electrode materials, can impede Li-ion transport, deteriorate performance, and eventually lead to cell failure. Here we leverage large-scale molecular simulations, enabled by validated machine-learning interatomic potentials, to directly probe the onset of interfacial degradation at the garnet Li7La3Zr2O12 (LLZO) solid-electrolyte/LiCoO2 (LCO) cathode interface. By surveying different interfacial geometries and compositions, it is found that Li-deficient interfaces can lead to severe interfacial disordering with cation mixing and Co interdiffusion from LCO into LLZO. By contrast, Li-sufficient interfaces are less disordered, although elemental segregation with local ordering is observed. As a consequence of Co interdiffusion, Co-rich regions are formed at the GBs of LLZO due to cation segregation and trapping effects. This behavior is independent of the GB tilting axis, degree of disorder at the GBs, and Co concentration, which implies Co clustering at GBs is a general phenomenon in polycrystalline LLZO and can dictate its overall transport and mechanical properties. Our findings elucidate the underlying fundamental mechanisms that give rise to experimentally observed physicochemical properties and provide guidelines for interface design that can mitigate interfacial degradation and improve cycling performance.

Glycolic acid doped PFN-Br as cathode interface to achieve high-efficiency in organic solar cells

Small compounds are often utilized to adjust the cathode interface of organic solar cells (OSCs) due to their low batch change, easy synthesis, unambiguous chemical structure, and low cost. In this work, the alcohol-soluble small molecule material Glycolic acid was doped into the electron transport material Poly(9, 9-bis(3′-(N, N-dimethyl)-N-ethylammoniumpropyl-2, 7-fluorene)-alt-2, 7-(9, 9-dioctylfluorene)) dibromide (PFN-Br) to modify the performance of the cathode interface layer (CIL). The CIL doped with Glycolic acid has better surface morphology, which is conducive to charge transport and extraction. In addition, the introduction of Glycolic acid improves the hydrophilicity of CIL, makes the metal electrode have good contact with CIL, and helps to improve the stability of the OSCs. Additionally, it suppresses the device's trap-assisted recombination and bimolecular recombination, hastening exciton dissociation and charge collection. As a result, the power conversion efficiency (PCE) of OSCs based on PM6: Y6 blend film has risen from 15.26 % to 15.91 %. After 312 hours of stability testing, the aforementioned doped devices still have device performance higher than standard device. Furthermore, based on PBDB-T: IT-M mix film, the PCE of the doped device and reference device was 11.29 % and 10.55 %, respectively. This study suggests that using the alcohol-soluble small-molecule material Glycolic acid can increase the organic solar cells' (OSCs') efficiency. This study provides a new method for manufacturing high-performance OSCs.

The Effect of Bi Addition on the Electromigration Properties of Sn-3.0Ag-0.5Cu Lead-Free Solder

As electronic packaging technology advances towards miniaturization and integration, the issue of electromigration (EM) in lead-free solder joints has become a significant factor affecting solder joint reliability. In this study, a Sn-3.0Ag-0.5Cu (SAC305) alloy was used as the base, and different Bi content alloys, SAC305-xBi (x = 0, 0.5, 0.75, 1.0 wt.%), were prepared for tensile strength, hardness, and wetting tests. Copper wire was used to prepare EM test samples, which were subjected to EM tests at a current density of approximately 0.6 × 104 A/cm2 for varying durations. The interface microstructure of the SAC305-xBi alloys after the EM test was observed using an optical microscope. The results showed that the 0.5 wt.% Bi alloy exhibited the highest ultimate tensile strength and microhardness, improving by 33.3% and 11.8% compared to SAC305, respectively, with similar fracture strain. This alloy also displayed enhanced wettability. EM tests revealed the formation of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) at both the cathode and anode interfaces of the solder alloy. The addition of Bi inhibited the diffusion rate of Sn in Cu6Sn5, resulting in similar total IMC thickness at the anode interface across different Bi contents under the same test conditions. However, the total IMC thickness at the cathode interface decreased and stabilized with increasing EM time, with the SAC305-0.75Bi alloy demonstrating the best resistance to EM.

Brominated Perylene Diimides as Cathode Interface Materials for High Efficiency Organic Solar Cells

AbstractThe cathode interface materials (CIMs) are crucial for organic solar cells (OSCs). Herein, excellent CIMs PDINN‐Br and PDINN‐2Br are reported, by bromination of PDINN. Both of them have strong work function (WF) tunability, self‐doping properties, and excellent film‐forming properties. They show higher electron mobility (over 2 × 10−4 cm2 V−1 s−1) and conductivity (≈5 × 10−5 S cm−1) than PDINN. Grazing‐incidence wide‐angle X‐ray scattering measurements (GIWAXS) illustrate that PDINN‐2Br has more ordered arrangement than PDINN and PDINN‐Br. PDINN, PDINN‐Br, and PDINN‐2Br in PM6:Y6‐based OSCs lead to 15.96%, 16.71%, and 17.03% power conversion efficiency (PCE), respectively. The PDINN‐2Br has well performance as well in the PM6:PYIT and D18:L8BO OSCs, PCEs of 18.14% and 18.98% are obtained, respectively, which are higher than PDINN (16.97% and 18.01%).

Synergistic Impact of Alloying with Ni on Cu Cathode Interfaces for Fluoride Batteries.

All-solid-state fluoride batteries have the potential to achieve energy densities significantly higher than those of lithium-ion batteries. A common cathode material for fluoride batteries is Cu. Cu has a low polarization, but its rapid capacity degradation due to grain growth and subsequent delamination from the solid-state electrolyte are critical issues. To enhance the performance of Cu-based cathodes in all-solid-state fluoride batteries, we explore alloying of Cu with Ni to create metastable solid solution phases (CuxNi1-x with x = 0, 0.32, 0.52, 0.72, 0.89, and 1.0). Compared to Cu, Ni has a higher polarization but exhibits superior capacity retention. The Cu0.72Ni0.28 alloy demonstrates a polarization as low as Cu, but it has a significantly improved capacity retention, which is comparable to Ni. Transmission electron microscopy observations demonstrate that the thin Ni-rich region formed near the interface inhibits Cu grain growth and delamination from the LaF3 electrolyte. By incorporating an appropriate amount of Ni into Cu, Cu-Ni alloy films combine the advantages of both metals, improving the performance of fluoride batteries.

Improve the cycling performance of solid-state sodium batteries through the design of a cathode interface buffering layer

The Na3Zr2Si2.2P0.8O12(NZSP) solid electrolyte has high room-temperature ionic conductivity, but issues at the cathode-electrolyte interface have impeded NZSP solid-state batteries development. This study employed a straightforward approach to create a Poly vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)-based gel buffer layer for the interface. By incorporating cathode active materials into the gel, the swelling compatibility and ionic conductivity were significantly enhanced. The prepared NGPEs (The name of the sample prepared by incorporating the cathode active material into the gel electrolyte.) membrane showed an ionic conductivity of 2.19 × 10−3 S/cm at room temperature and reduced the NFM||NGPEs-2-NZSP||Na battery’s interface impedance by 80 %. This protection enhances the reversible capacity of the battery during charging and discharging processes, and improves the cycling stability of the battery. The advancement presents a novel strategy for the operation of solid-state batteries at room temperature.

Ion-Anchored Strategy for MnO2/Mn2+ Chemistry without "Dead Mn" and Corrosion.

The utilization of MnO2/Mn2+ chemistry in near-neutral pH acetate aqueous electrolytes provides an opportunity to achieve a higher energy density (theoretical capacity 616 mA h/g, discharge platform >1.5 V). However, this Zn-MnO2 aqueous battery suffers from inevitable "dead Mn" and proton corrosion. In this study, we discover that the diffusion of the cathode reaction intermediate Mn3+ is intrinsic for the generation of "dead Mn", and the accumulation of "dead Mn" increases the H+ which shuttles to the anode, inducing serious corrosion. A pH-neutral hydrogel ion-anchored strategy is proposed here not only to restrict the diffusion of Mn3+ but also to suppress the proton transference. This hydrogel ion anchor is designed by deprotonating a series of monomers undergoing in situ free radical polymerization at the cathode interface. The anionic monomer with a moderate binding energy to manganese ions is screened to anchor Mn3+, which enhances the reversibility of the MnO2/Mn2+ reaction. Simultaneously, a substantial amount of anionic groups and hydrophilic functional groups in the hydrogel effectively constrains the proton shuttle to corrode the anode. Consequently, the Zn/MnO2 battery achieves exceptional cyclic stability of the MnO2/Mn2+ reaction, sustaining 8500 cycles even at a relatively low current density and discharge current density of 1 mA/cm2. Our findings highlight the importance of anchoring Mn3+ at the cathode interface and offer valuable insights for advancing practical applications of MnO2/Mn2+ reactions.

Toward Practical Li–S Batteries: On the Road to a New Electrolyte

AbstractThe lithium–sulfur (Li–S) battery system has attracted considerable attention due to its ultrahigh theoretical energy density and promising applications. However, with the increasing demands on S loading and electrolyte content, practical Li–S batteries still face several serious challenges, such as slow reaction kinetics at the cathode interface, unstable anode interface reactions, and undesirable crosstalk effects between the cathode and anode. Traditional electrolyte systems often struggle to address these challenges under practical conditions, thereby rendering it imperative to establish a new electrolyte system for practical Li–S batteries. This review first discusses the necessity of establishing a new electrolyte and propose specific parameter requirements, such as the electrolyte‐to‐sulfur mass ratio (Em/S). Subsequently, some electrolyte modification strategies proposed by researchers are summarized to address the different challenges associated with practical Li–S batteries. Finally, the combination of different strategies is reviewed, aiming to reveal more effective design approaches that simultaneously address multiple challenges, while providing guidance for establishing a new balanced electrolyte for practical Li–S batteries. This article promotes the development of new electrolytes for practical Li–S batteries and can act as a reference for the development of electrolytes for other secondary batteries.

Application of isoindigo-based small molecule conjugated electrolytes at interfaces with organic solar cells

Zwitterionic small molecule materials are widely employed in the cathode interface layer of organic solar cells (OSCs). Nevertheless, the exploration of superior cathode interface materials with the objective of enhancing the performance of OSCs remains a significant challenge. Two water/alcohol soluble n-type self-doped small molecule conjugated electrolytes were synthesized using isoindigo as the acceptor unit and triphenylamine (TPA) as the donor unit. Quaternary ammonium salts or pyridine salts were used as the polar side chains. When applied to organic solar cells (OSCs) with PTB7-Th: PC71BM as the active layer, the devices showed improved performance. The power conversion efficiency (PCE) reached 8.59 % (IIDN2TPA) and 8.81 % (IIDPy2TPA), respectively. These results demonstrate the water/alcohol-soluble D-A-D-type small-molecule conjugated electrolytes offer an effective strategy in designing cathode interlayer (CIL) and preparing the high-performance OSCs.

Novel self-doping alcohol-soluble quinacridone-based small molecule at the cathode interface layer of organic solar cells

Interfacial modification plays a crucial part in improving the photovoltaic performance and stability of organic solar cells (OSCs). The self-doping effect can enhance the inter-ohmic contact at the active layer material with the cathode. Therefore, we synthesised a self-doping alcohol-soluble quinacridone-based small molecule, 5,12-bis(3-(dimethylamino)propyl)-5,12-dihydroquinolo[2,3-b]acridine-7,14-dione (QAN), with a self-doping effect, and introduced QAN as cathode interfacial layers (CILs) into OSCs. The central nuclear structure of QAN is an electron-deficient unit with a large conjugated structure. This structure facilitates electron transport as a cathode-interface material. Additionally, its polar side chains enhance the solution-processing capability and contribute to a more pronounced self-doping effect. Compared with the devices without interfacial material, the open-circuit voltage(VOC) and short-circuit current (JSC) with QAN as an interfacial material increased. What's more, the optimal photoelectric conversion efficiency (PCE) of the QAN CIL device is increased to 9.05 % for the same experimental conditions, which is 40 % higher than the device without interface material. By characterizing the surface morphology, it was found that the PTB7-Th:PC71BM active layer devices exhibited a smooth surface morphology and improved hydrophilicity when inserted with QAN CIL, which helps to enhance the physical contact of the active layer with the cathode, in addition to charge extraction and transport. This result suggests that introducing QAN as the CILs of the device is a viable way to improve the performance of the OSCs.

Multifunctional Scavenger Boosts Cathode Interfacial Stability with Reduced Water Footprint for Direct Recycling of Spent Lithium-Ion Batteries.

The burgeoning accumulation of spent lithium-ion batteries (LIBs), a byproduct from the widespread adoption of portable electronics and electric vehicles, necessitates efficient recycling strategies. Direct recycling represents a promising strategy to maximize the value of LIB waste and minimize harmful environmental outcomes. However, current efforts to large-scale direct recycling face challenges stemming from heterophase residues (e.g., Li2CO3, LiOH) in the recycled products and uncontrolled interfacial instability, often requiring repeated washing that generates significant wastewater. Here, a refined direct recycling process is proposed to improve cathode interface stability by leveraging in situ reaction between surface residual lithium species and a weak inorganic acid to form a conformal Li+ conductive coating that stabilizes the regenerated Ni-rich cathodes with significantly reduced water footprint. The findings reveal that the conductive coating also prevents direct contact between contaminants and the cathode surface, thus improving the ambient storage stability. By eliminating the need for extensive washing, this intensified recycling process offers a more sustainable approach with the potential to transition from laboratory to industrial-scale applications, improving both product quality and environmental sustainability.

High Performance All‐Solid‐State Lithium Batteries: Interface Regulation Mechanism

AbstractAll‐solid‐state lithium batteries (ASSLBs) can overcome many problems in cathode and lithium anode, and it is a very promising safe secondary battery. However, unstable interface problems between electrolyte and electrode and within the electrolyte still restrict its commercial development. Herein, the interface problems are first revealed in ASSLBs and highlight the need to deeply explore the intrinsic failure mechanisms to solve these problems. Subsequently, the three failure mechanisms of ASSLBs: chemical, electrical, and electrochemical failure are broken down, and focus on the impact of the space charge layer problem on the cathode‐electrolyte interface. The effect of the anode physical contact problem on the anode‐electrolyte interface is discussed. Then, recent advances in ASSLBs, cathode and anode interface optimization strategies, and their corresponding electrochemical properties are discussed. Finally, the interface challenges faced by ASSLBs and feasible interface modification strategies are summarized, which provide references for subsequent studies and insights into the design of interface structures for the new generation of high‐performance ASSLBs.