Multifunctional Binders Research Articles

(Invited) Multifunctional Binders for High-Performance Rechargeable Batteries

Secondary battery plays a significant role in our daily life as well as in modern smart grids, which typically consists of an electrolyte and two electrodes determining the key parameters of the battery. Despite a small dose that usually less than 10%, the binder is a crucial component to keep the electrode integrity and ensure the high electrochemical performance. What`s more, the modification of binder could be conducted to alleviate or even eliminate the side effects raised by failure behaviors of the electrode active materials. However, the state-of-the-art binder optimization strategies still fall behind the rapid development of the novel electrode materials.To improve the energy density of secondary batteries, high-capacity electrode materials have been explored, including silicon, sulfur, layered oxides, etc. However, their practical applications are hindered by various failure behaviors. Take Si as an example, though the Si-based anodes exhibit high capacity up to 4200 mA g-1, they undergo huge volumetric expansion (≈400%) during the electrochemical reactions, resulting in the cracking of active material particles, electrode exfoliation, continuous electrolyte consumption and progressive SEI formation. As a consequence, the capacity of Si-based electrode decreases dramatically along with cycling. The conventional binders that have been widely used in the rechargeable battery systems are typically linear polymers, which are unable to endure the high volume change and address other challenges raised by electrode materials such as low conductivity, unstable bulk structure and interface, etc. To increase the mechanical strength and the electrochemical stability of electrodes, the design of multi-functional binders is considered to be an effective strategy to meet various requirements of advanced binders for high-performance batteries simultaneously.In this work, the synthesis and characterization of multifunctional binders for high-capacity electrode materials are demonstrated. By the introduction of intermolecular forces and chemical bonds, 3D networks are constructed and the ability for volume change accommodation are enhanced as well as the binding force. Moreover, the dynamic crossed links also endow the binders with self-healing ability, which could help to remedy the cracking issues in the advanced electrode materials. Due to the merits of the as-synthesized binders, the electrochemcial performance of the high-capacity electrode is significantly improved, demonstrating a promising strategy for next-generation energy storage systems.

Recent Advances in Multifunctional Binders for High Sulfur Loading Lithium‐Sulfur Batteries

AbstractLithium‐sulfur batteries (LSBs) are regarded as a highly promising next‐generation energy storage technology due to their exceptional theoretical capacity and energy density. However, the practical application of these batteries is hindered by several challenges, including significant volume change of active materials, severe shuttle effect of lithium polysulfides, inadequate electronic and ionic conductivity, and safety concerns. These issues are particularly pronounced in cathodes with high sulfur loading, which are essential for the effective implementation of LSBs. Binders are an essential constituent of sulfur cathodes, and they perform a crucial function in enhancing the efficacy of LSBs, particularly when subjected to high sulfur loading. A considerable amount of research has been conducted to investigate the potential of multifunctional binders to tackle the aforementioned challenges associated with LSBs. This article provides a comprehensive overview of the various roles that advanced multifunctional binders play in LSBs, including but not limited to preserving electrode integrity, capturing lithium polysulfides, regulating Li2S deposition, accelerating reaction kinetics, enhancing ionic and electronic conductivity, promoting sulfur cathode safety, and safeguarding the environment. Additionally, the paper outlines the challenges and prospects for future research endeavors aimed at creating innovative multifunctional binders and improving the overall performance of LSBs.

Self-Repairable Silicon Anodes Using a Multifunctional Binder for High-Performance Lithium-Ion Batteries.

Despite of extremely high theoretical capacity of Si (3579 mAh g-1 ), Si anodes suffer from pulverization and delamination of the electrodes induced by large volume change during charge/discharge cycles. To address those issues, herein, self-healable and highly stretchable multifunctional binders, polydioxythiophene:polyacrylic acid:phytic acid (PEDOT:PAA: PA, PDPP) that provide Si anodes with self-healability and excellent structural integrity is designed. By utilizing the self-healing binder, Si anodes self-repair cracks and damages of Si anodes generated during cycling. For the first time, it is demonstrated that Si anodes autonomously self-heal artificially created cracks in electrolytes under practical battery operating conditions. Consequently, this self-healable Si anode can still deliver a reversible capacity of 2312mAhg-1 after 100 cycles with remarkable initial Coulombic efficiency of 94%, which is superior to other reported Si anodes. Moreover, the self-healing binder possesses enhanced Li-ion diffusivity with additional electronic conductivity, providing excellent rate capability with a capacity of 2084 mAh g-1 at a very high C-rate of 5 C.

Reversible cross-linked phosphorylate binder for recyclable lithium-sulfur batteries

The development of facile and eco-friendly recycling strategies for lithium-sulfur batteries (LSBs) is very important since they will generate a growing hazard to the environment. Herein, a hydrogen bonding cross-linked multi-functional binder (named: APL) of Lithiated polyacrylic acid-co-vinylphosphonic acid (AA-VPA) and phosphorylated soy protein (P-SPI) is explored for LSBs. Owing to the precipitation of P-SPI at the isoelectric point, hydrogen bonding cross-linking between AA-VPA and P-SPI can be readily dissociated under acidic conditions, providing a facile method to enable SC composite recycled by a convenient acid pickling. Moreover, the robust cross-linking network provides APL binder a strong bonding force and excellent mechanical properties, ensuring the structural integrity of the sulfur (S) electrode during long-term cycling. The abundant polar groups within APL polymeric network endow sulfur cathode with superior polysulfide anchoring capacity and retard the shuttle effect of LSBs. APL-based sulfur cathode rendered a high specific capacity of 940 mAh g−1 with a sulfur loading of 4.8 mg cm−2. After 250 charge/discharge cycles at a current density of 1C, the specific capacity of sulfur cathode is still as high as 805 mAh g−1. Hence, the flexible electrode remains intact after bending. This work proposes an environment-friendly and cost-effective strategy for the development of reversible cross-linked multi-functional binders for recyclable and high-energy LSBs.

A polysulfide radical anions scavenging binder achieves long‐life lithium–sulfur batteries

AbstractFast capacity decay caused by the polysulfide shuttle is the primary cause to impede the practical application of lithium–sulfur (Li–S) batteries. The polysulfide shuttle involves the evolution of polysulfide dianions (Li2Sx, x = 3–8) and radical anions (Sn•–) during the charge‐discharge process. Despite good efforts have been made to suppress polysulfide shuttle, the electrolyte depletion caused by the attack of polysulfide radical anions, which results in rapid battery aging, has been almost ignored. To address this challenge, based on a two‐prolonged design philosophy, we demonstrate a polylysine‐derived cathode binder with a free radical‐scavenging function, lipoic acid‐grafted ε‐polylysine (EPL‐g‐Lipo), where abundant amide and amine groups in the ε‐polylysine component possess a high polysulfide affinity, while lipoic acid motifs offer an excellent polysulfide radical anions‐scavenging ability. As a result, Li–S batteries with EPL‐g‐Lipo binder display superior cycling stability to poly(vinylpyrrolidone) binder‐based counterparts, mainly ascribed to its powerful shuttle suppression effect and free radicals scavenging ability. This study states the importance of designing multifunctional binders for performance improvements of Li–S batteries.

Water-Soluble Conductive Composite Binder for High-Performance Silicon Anode in Lithium-Ion Batteries

The design of novel and high-performance binder systems is an efficient strategy to resolve the issues caused by huge volume changes of high-capacity anodes. Herein, we develop a novel water-soluble bifunctional binder composed of a conductive polythiophene polymer (PED) and high-adhesive polyacrylic acid (PAA) with abundant polar groups. Compared with conventional conductive additives, the flexible conductive polymer can solve the insufficient electrical contact between active materials and the conductive agent, thus providing the integral conductive network, which is extremely important for stable electrochemical performance. Additionally, the polar groups of this composite binder can form double H-bond interactions with the hydroxyl groups of SiO2 layers onto the silicon surface, keeping an integral electrode structure, which can decrease the continuous formation of SEI films during the repeated cycles. Benefiting from these bifunctional advantages, the Si electrodes with the composite binder delivered a high reversible capacity of 2341 mAh g−1 at 1260 mA g−1, good cycle stability with 88.8% retention of the initial reversible capacity over 100 cycles, and high-rate capacity (1150 mAh g−1 at 4200 mA g−1). This work opens up a new venture to develop multifunctional binders to enable the stable operation of high-capacity anodes for high-energy batteries.

Lithium substituted poly(amic acid) as a water-soluble anode binder for high-temperature pre-lithiation

Multifunctional binders hold great promise in advanced electrode designs for both fundamental research and practical utilization of lithium-ion batteries (LIBs). The reactions between Si/SiO x -dominated anodes with lithium are expected to be exothermic in principle, while the thermal tolerance along with the volume change makes high-temperature binders attractive for large scale roll-to-roll manufacturing. For instance, if a high temperature binder is also water soluble, it can be compatible with the current graphite-based anode manufacturing process. In this work, we present a water-soluble poly(amic acid)-based binder, which can withstand high temperature for industrial pre-lithiation process and effectively hold active materials together during repeated charge and discharge cycles. This lithium substituted poly(amic acid) binder (denoted as Li-Pa) can serve as a drop-in replacement for environmentally friendly electrode fabrication in large scale by providing aqueous solubility, exceptional thermal stability and mechanical flexibility. • A water-soluble lithium substituted poly(amic acid) binder was designed for Si electrodes. • Thermal imidization of lithium substituted poly(amic acid) to polyimide was achieved. • Polyimide binder based Si electrodes are thermally stable up to 500 °C. • High temperature pre-lithiation can be performed on these electrodes.

Water Reducer: A Highly Dispersing Binder for High‐Performance Lithium‐Sulfur Batteries†

Main observation and conclusionSulfur has been paid close attention by the research and manufacturing as a cathode material for lithium‐sulfur batteries (LSB) in recent decade because it has high specific capacity and low cost. But the low utilization of active materials and serious shuttle phenomenon inhibit its commercialization process. In this work, for the first time, water reducers are reported as multifunctional binders to address the above problems to enhance the performance of LSB. Due to the synthetic actions of the water reducer binder, such as highly dispersing effect and good chemical trapping function, commercial sulfur powders are directly used as cathodes, and much better electrochemical performance compared to using the conventional binder polyvinylidene fluoride (PVDF) was obtained, among which the sulfur cathode with sulfonated melamine formaldehyde (SMF) water reducer binder exhibits a high reversible capacity of 625.5 mA·h·g–1 after 200 cycles at 1 C and the cathode with polycarboxylic acid (PC) water reducer binder even demonstrates a high area specific capacity of 5 mA·h·cm–2 at high sulfur loading of 5 mg·cm–2. These low‐cost water reducers are a promising binder for LSB in the future.

2,2-Dimethyl-1,3-dioxane-4,6‑dione functionalized poly(ethylene oxide)-based polyurethanes as multi-functional binders for silicon anodes of lithium ion batteries

Chemically reactive groups (2,2-dimethyl-1,3-dioxane-4,6‑dione (Meldrum's acid, MA) and poly(ethylene oxide) (PEO) segments are incorporated to polyurethanes as binders of silicon anode for lithium ion batteries, aiming to address the volume change issue of the silicon anode in lithiation/delithiation cycles. The polymeric binder builds up multiple interaction to silicon surfaces, including hydrogen bonding between the urethane linkages of the bonder and silanol groups of silicon surfaces and covalent linkages through the addition reaction between ketene groups (generated from MA thermolysis reaction) and silanol groups of silicon surfaces. Self-dimerization of ketene groups also results in crosslinked structure of the binder. Both of the above-mentioned interaction and crosslinked structure contribute to stabilize the silicon anode materials. Moreover, the PEO segments facilitate the transportation of lithium ions and increase the ion conductivity of the anode. Consequently, the corresponding silicon anode is workable at a high C rate (0.8C) to demonstrate a specific capacity of approximately 1,785 mAh g − 1 and a capacity retention of 58% after a 600-cycle charge/discharge test. Morphological observation on the anode materials after a 300-cycle test indicates that the reactive PU binder could effectively depress cracks and interphase separation of the anode materials caused by the lithiation/delithiation-induced volume changes. The prepared binder also exhibits stabilization on the solid electrolyte interphase (SEI) layer and prevent anode material delamination. The results demonstrate a successful example of designs and preparation of multi-functional binders for silicon anodes.

Environmentally Friendly Binders for Lithium‐Sulfur Batteries

AbstractLithium‐sulfur batteries (LSBs) have attracted the battery community's attention in recent years because of the ultra‐high theoretical specific capacity and energy density. To realize the commercial application of LSBs, issues including lithium polysulfide shuttle effects, insulating active materials, and large volume changes are urgently to be solved, especially LSBs with high sulfur loading suffering from more serious capacity fading. Developing environmentally friendly and multifunctional binders would not only overcome the problems existing in LSBs but could also satisfy the requirements for green materials. In this Review, we first conclude the required characteristics for binders in LSBs, then summarize the research progress of ecofriendly binders in detail, as well as outstanding binders applied in high‐sulfur‐loading electrodes. Finally, the challenges and development direction of binders for future industrial applications in LSBs are also highlighted.

Influence of Binder Coverage on Interfacial Chemistry of Thin Film LiNi0.6Mn0.2Co0.2O2 Cathodes

In this work, we explore the influence of binder coverage and chemistry on the interfacial properties of the textured Ni-rich cathode LiNi0.6Mn0.2Co0.2O2. We find that the formation of the cathode/electrolyte interphase (CEI) composition varies significantly for cathodes coated with either poly(vinylene fluoride) (PVDF), carboxymethyl cellulose (CMC), or lithium polyacrylate (LiPAA) after cycling to high upper cutoff voltages (4.5 V vs Li/Li). The PVDF-coated samples had a thinner CEI and twice the relative concentration of LiF and Li2CO3 to LixPOyFz species in the CEI compared to the uncoated sample. This correlated with significantly lower interfacial impedance (285 vs ∼1700 Ohm-cm2) and improved capacity retention between cycles of the PVDF-coated samples compared to the other binder compositions and the uncoated sample. CMC-coated samples performed worst, with a CEI comprised of greater amounts of LixPOyFz. In addition, we find the choice of binder results in the selective protection or promotion of electrolyte reactions at the (104) surface of the 622 cathode. This suggests that the choice of binder can impact the surface chemistry and performance of high voltage cathodes and supports an avenue for interest in multifunctional binders for stabilizing the CEI.

Novel multi-block conductive binder with polybutadiene for Si anodes in lithium-ion batteries

Using conductive binders, instead of the traditional binders and conductive additives, is an effective way to increase the specific capacity and long cycle life of the silicon (Si) anode. However, the rigid conductive binders of Si anodes tend to form cracks during the repetitive huge volume changes of Si. Here, a novel n-type conductive binder, multi-block polymer of poly(1-pyrenemethyl methacrylate) and polybutadiene (PPy-b-PB) was designed. The polybutadiene (PB) rubber was incorporated into the conductive binder by combining condensation and reversible addition-fragmentation chain transfer polymerization. With high initial coulombic efficiency of 77.9%, the PPy-b-PB/Si anode possesses high reversible capacity (2274 mAh g−1) and capacity retention (87.1%) at the rate of 0.2 C (0.84 A g−1) after 200 cycles. The superior cyclic performance of the PPy-b-PB can be ascribed to the PB rubber, which enhanced the reversible deformation ability, flexibility, and adhesion length scale of the binder, without with a negligible change of the charge-transfer resistance for the anode. The original structure and the preparation method of the multi-block conductive binder provide a new way to manufacture multifunctional binders.

Material and Structural Design of Novel Binder Systems for High-Energy, High-Power Lithium-Ion Batteries

Developing high-performance battery systems requires the optimization of every battery component, from electrodes and electrolyte to binder systems. However, the conventional strategy to fabricate battery electrodes by casting a mixture of active materials, a nonconductive polymer binder, and a conductive additive onto a metal foil current collector usually leads to electronic or ionic bottlenecks and poor contacts due to the randomly distributed conductive phases. When high-capacity electrode materials are employed, the high stress generated during electrochemical reactions disrupts the mechanical integrity of traditional binder systems, resulting in decreased cycle life of batteries. Thus, it is critical to design novel binder systems that can provide robust, low-resistance, and continuous internal pathways to connect all regions of the electrode. In this Account, we review recent progress on material and structural design of novel binder systems. Nonconductive polymers with rich carboxylic groups have been adopted as binders to stabilize ultrahigh-capacity inorganic electrodes that experience large volume or structural change during charge/discharge, due to their strong binding capability to active particles. To enhance the energy density of batteries, different strategies have been adopted to design multifunctional binder systems based on conductive polymers because they can play dual functions of both polymeric binders and conductive additives. We first present that multifunctional binder systems have been designed by tailoring the molecular structures of conductive polymers. Different functional groups are introduced to the polymeric backbone to enable multiple functionalities, allowing separated optimization of the mechanical and swelling properties of the binders without detrimental effect on electronic property. We then describe the design of multifunctional binder systems via rationally controlling their nano- and molecular structures, developing the conductive polymer gel binders with 3D framework nanostructures. These gel binders provide multiple functions owing to their structure derived properties. The gel framework facilitates both electronic and ionic transport owing to the continuous pathways for electrons and hierarchical pores for ion diffusion. The polymer coating formed on every particle acts as surface modification and prevents particle aggregation. The mechanically strong and ductile gel framework also sustains long-term stability of electrodes. In addition, the structures and properties of gel binders can be facilely tuned. We further introduce the development of multifunctional binders by hybridizing conductive polymers with other functional materials. Meanwhile mechanistic understanding on the roles that novel binders play in the electrochemical processes of batteries is also reviewed to reveal general design rules for future binder systems. We conclude with perspectives on their future development with novel multifunctionalities involved. Highly efficient binder systems with well-tailored molecular and nanostructures are critical to reach the entire volume of the battery and maximize energy use for high-energy and high-power lithium batteries. We hope this Account promotes further efforts toward synthetic control, fundamental investigation, and application exploration of multifunctional binder materials.

Strong affinity of polysulfide intermediates to multi-functional binder for practical application in lithium–sulfur batteries

Binder, one of the most important battery components, plays a critical role in lithium–sulfur batteries. Poly(vinylidene difluoride) (PVDF), a commonly used binder in lithium–sulfur batteries, does not have a strong affinity to the intermediate polysulfides, however, leading to fast capacity fading with electrochemical cycling. Herein, copolymers of vinylidene difluoride with other monomers are used as multi-functional binders to enhance the electrochemical performance of lithium–sulfur batteries. Compared to the PVDF, the copolymer, poly(vinylidene difluoride-trifluoroethylene) (P(VDF-TRFE)) binder exhibits higher adhesion strength, less porosity, and stronger chemical interaction with polysulfides, which helps to keep the polysulfides within the cathode region, thereby improving the electrochemical performance of the lithium–sulfur battery. As a result, sulfur electrode with P(VDF-TRFE) binder delivered a high capacity of 801mAhg−1 at 0.2C after 100 cycles, which is nearly 80% higher capacity than the corresponding sulfur cathode with PVDF binder.

Ionically‐Functionalized Poly(thiophene) Conductive Polymers as Binders for Silicon and Graphite Anodes for Li‐Ion Batteries

AbstractNext‐generation anode materials for Li‐ion batteries such as silicon can lead to ten times more capacity than the state‐of‐the‐art graphite. However, novel binders are required to overcome the detrimental effects of volume changes during battery cycling of silicon because of the poor chemical interaction and electrical conductivity between silicon and the binder. Most studies focus on either ionic binders or electrically conductive binders, but herein it was demonstrated that a new family of polymers based on electrically conductive poly(thiophene) functionalized with an ionic alkyl carboxylate groups of various lengths can successfully work as multifunctional binders for silicon and commercial graphite anodes in Li‐ion battery half‐cells. It was determined that the polymer with shorter side chain (PT‐3‐LiA) gives the highest reversible capacity upon pairing with graphite or silicon, reaching 3000 mAh g−1 in the case of the latter, a capacity 500 mAh g−1 (≈22 %) higher than those obtained with the electrically, but non‐ionically, conductive PEDOT:PSS binder and the ionically, but non‐electrically, conductive sodium carboxymethyl cellulose (NaCMC) binder. It is demonstrated that the superior performance of this new type of multifunctional binders can be attributed to their ability to maintain their doping level and conductivity as well as due to good interaction with the silicon surface during cycling.

Light-induced Polymer- and Polymerization Reactions, Part 43, Aqueous Developable Cationic Photopolymer Systems—Characteristic Curves and Kinetics

AbstractNew photopolymer systems are described consisting of multifunctional epoxide monomers, photoinitiators and polymeric binders containing carboxyl groups. The photoinitiators contain two components: sensitizer (light absorbing component) and diaryliodonium salt. The exposed areas become insoluble in weak alkaline aqueous developer. The network formation process has been measured by the insoluble fraction (gel fraction) of the cured photopolymer system as a function of the exposure energy, i.e. by the characteristic curve. The two main parameters of these curves, gel point exposure energy and contrast factor, depend on the composition of the system. Mainly, the ingredients of the photoinitiator and their concentration influence the network formation process.