Silicon Anodes In Lithium-ion Batteries Research Articles

Structure and Stability of the Solid Electrolyte Interphase on Silicon Anodes of Lithium-Ion Batteries

The solid electrolyte interphase (SEI) acts as a protection layer on the surface the anodes of lithium ion batteries to prevent further electrolyte decomposition. Understanding the fundamental properties of the SEI is essential to the development of high capacity silicon anodes. However, the detailed mechanism of the generation of the evolution of the SEI on the silicon anodes is not fully understood. This manuscript reviews our recent investigations of the SEI on silicon anodes. We have studied the fundamental formation mechanism of the SEI on silicon anodes, along with the evolution which occurs to the SEI upon cycling.

Design of high-energy-dissipation, deformable binder for high-areal-capacity silicon anode in lithium-ion batteries

• The efficient energy-dissipation binder is harnessed on silicon anodes. • A synergized static and dynamic strategy is used to release the stress. • The mechanism is clarified by in-situ IR and finite element simulations. • Unprecedented cycling performances are achieved at high areal capacity. Although silicon has the highest theoretical capacity among the existing anode materials, its practical application is highly hindered by huge interface stress arising from large volume change upon cycling. Herein, an efficient energy-dissipation engineering was harnessed on high-capacity silicon anodes through a synergized “static” (chemically crosslinking) and “dynamic” (physically crosslinking) binder. In this dual network, the disassociation of non-covalent hydrogen bonds greatly facilitates the dispersion and release of unfavorable stress, while the permanent chemical bonding network enables a deformable network to sustain the electrode structure. Such a strategy effectively avoids both materials and electrodes deterioration and promises a better Si-based anode: a high areal capacity of 2 mAh cm −2 with capacity retention of 91.3% after 200 cycles. Meanwhile, the energy-dissipation mechanism was further clarified by temperature-dependent FTIR and finite element simulations.

Polysaccharide-based self-healing polymer binder via Schiff base chemistry for high-performance silicon anodes in lithium-ion batteries

The use of crosslinked glycol chitosan (GCS) is explored as an efficient, low-cost, eco-friendly, and water-soluble polymer binder for Si anodes in lithium-ion batteries (LIBs). A supramolecular, self-healing 3D network is constructed between the amino groups in glycol chitosan and the dialdehyde groups of oxidized alginate (OSA) through dynamic Schiff base reactions. The oxidized alginate crosslinker spontaneously reacts with the natural polymer to form an imine bond, which leads to the formation of a supramolecular network. This mechanism provides this polymer binder with strong and dynamic covalent bonding for Si anodes (GCS-I-OSA), which can effectively buffer the large volume changes in Si that occur during the lithiation/delithiation process. The obtained GCS-I-OSA-10 binder-based Si anode exhibited excellent electrochemical performance, with a high degree of reversibility (2316 mAh g−1 at 0.2 C after 100 cycles). In addition, the GCS-I-OSA-10 electrode exhibited excellent rate performance, achieving high reversibility (2185 mAh g−1 at a high current density of 5C) and high long-term cycling stability (1507 mAh g−1 after 200 cycles), even at a high current density (1C). Moreover, even when applied to commercial Si/graphite composite anodes, this GCS-I-OSA-10 binder was able to deliver superior cycle performance (with a specific capacity of 1364 mAh g−1 at a current density of 0.2 C after 100 cycles), demonstrating excellent potential for practical applications in LIBs.

A carboxymethyl vegetable gum as a robust water soluble binder for silicon anodes in lithium-ion batteries

The dramatic volume change and electrode pulverization hinder the practical utilization of silicon-based anodes for lithium-ion batteries. Studies show that binders can be an effective approach to solve these issues. Herein, the natural vegetable gum-guar gum (GG) is modified through carboxymethylation method. The carboxymethyl guar gum (CMGG) exhibits rapid water solubility, excellent thermal stability, high viscosity and robust adhesion. When it is applied as a binder for silicon anodes, the CMGG possessing affluent hydroxyl and carboxyl groups can effectively accommodate the significant volume variations of silicon particles through the formation of intensive hydrogen bonds. The Si @ CMGG electrode not only retains a high reversible capacity of 1865 mAh g−1 after 200 cycles with a capacity decay rate of 0.12% for each cycle, but also holds a capacity of 1287.1 mAh g−1 after 100 cycles with high mass loading of 1.15 mg cm−2. Furthermore, the CMGG binder can promote the lithium-ion transport like guar gum and reduce the electrode polarization, which is helpful in maintaining the electrochemical stability of Si anodes at high current density.

Dual Cross-Linked Polymer Networks Derived from the Hyperbranched Poly(ethyleneimine) and Poly(acrylic acid) as Efficient Binders for Silicon Anodes in Lithium-Ion Batteries

The condensation of poly(acrylic acid) (PAA) with small amounts of hyperbranched poly(ethyleneimine) (PEI) resulted in the dual cross-linked network cxPAA-PEI(x) (x: wt % of PEI, x = 1, 3, and 5), ...

TEMPO-oxidized cellulose nanofibers as versatile additives for highly stable silicon anode in lithium-ion batteries

Silicon (Si) has been considered the most promising anode material for next-generation lithium-ion batteries due to its high theoretical capacity and natural abundance. However, the Si anode suffers from massive volume change, which results in challenging cycling performance. Many researches demonstrated that polymeric binder plays an important role to sustain the structural integrity of Si anodes. While most studies about the binder material have been focused on enhancing distinctive properties such as adhesive strength and mechanical property, it has been recently shown that binder distribution can help to improve electrochemical performance. Herein, we introduce TEMPO-oxidized cellulose nanofiber (TOCNF) as a versatile additive for the binder of silicon anode. The one-dimensional morphology of TOCNF efficiently reinforces the mechanical properties of the electrode. The TOCNF additive also contains carboxylic groups with sufficient flexibility to induce intimate interaction with Si via hydrogen bonding. Based on all of these beneficial features of TOCNF, the addition of ~ 1 wt% of TOCNF of the whole weight of silicon anode slurry significantly improved cycling stability. With pre-mixing, the resulting Si-TOCNF allows efficient water-based binder solution penetration, thus improving uniform binder distribution of electrode. Furthermore, the well-distributed binder protects silicon surface and forms a stable SEI layer. The current study suggests that the TOCNF additive facilitates uniform binder distribution in the electrode with enhanced mechanical properties, leading to improved cycling performance.

Restorable Neutralization of Poly(acrylic acid) Binders toward Balanced Processing Properties and Cycling Performance for Silicon Anodes in Lithium-Ion Batteries.

Neutralization of poly(acrylic acid) (PAA)-based binders using lithium hydroxide is a common strategy for fabricating silicon anode laminates, which improves rheological properties of slurries toward high-quality electrode laminates. However, the significantly increased basicity causes degradation of Si particles while the irreversible conversion of carboxylic acid groups to lithium carboxylates undermines the binding strength, collectively leading to adverse cycling performance of the fabricated Si anodes. Herein, a novel neutralization process for PAA binders is developed. A weak base, ammonia (NH3), was discovered as a neutralizing agent that still promotes rheological response of binder solutions but results in a reduced pH increase. Interestingly, the resulting ammonium carboxylate groups may cleave during the drying process to restore the neutralized PAA (PAA-NH3) binders to their pristine states. The best-performing composition of 50% neutralization (PAA-50%NH3) provides comparable rheological response as a PAA-Li binder as well as much improved cycling performance. The half-cells using the PAA-50%NH3 binder can deliver 60% capacity retention over 100 cycles at C/3 rate, affording a 23.8% increase compared to PAA-Li half-cells. This restorable neutralization process of PAA binders represents an innovative strategy of mitigating issues from slurry processing of Si particles to achieve concurrent improvements in high-quality lamination and cycling performance.

Epoxy and amide crosslinked polarity enhanced polysaccharides binder for silicon anode in lithium-ion batteries

Natural polysaccharides are considered to be effective binders to enhance the cycle stability of silicon anode of lithium-ion batteries. However, the poor mechanical strength and relatively low binding strength have limited its further application. Epoxy and amide groups are recognized as the organic crosslinker with high polarity, which could bring qualified mechanical and binding strength. Herein, a crosslinked copolymer konjac glucomannan-g-polyacrylamide-g-glycidyl methacrylate (KPG) has been synthesized by radical polymerization reaction and applied as an aqueous binder for silicon anode materials. The introduction of polyacrylamide (PAM) and glycidyl methacrylate (GMA) improved the mechanical strength and binding strength through their high polarity and crosslinked effect. As a result, excellent electrochemical performance (capacity of 1415 mAh g−1 after 200 cycles at 0.2 C) was obtained by using the crosslinked network binder. The lithium insertion capacity of the silicon electrode was limited to 1000 mAh g−1, which can maintain 650 cycles. This reasonable design provides a way for the manufacture and practical application of high-performance silicon-based anodes.

Ternary Cross-Linked Multi-Functional Blended Polymers for High-Performance Silicon Anodes in Lithium-Ion Batteries

Silicon (Si) based anode material is highly attractive for next-generation lithium‐ion batteries (LIBs) due to its unparalleledtheoretical capacity and abundance. However, a severe problem of Si is the significant volume change associated with thelithiation processes, resulting in reduced capacity retention. Researchers have traditionally considered the roles ofinteractive binders and conductive additives as separate entities. These two components often lead to remarkablydecreased mass ratio of Si to nonactive material, which inevitably limits the electrode capacity. To achieve an enhanceutilization efficiency, herein, we have developed a multifunctional nanocomposite binder for high capacity nano-size Sibasedmaterial through a cross-linked polymer of carboxymethylcellulose (CMC), polyacrylic acid (PAA) spine withgraphenized polyacrylonitrile (PAN) through a gradual carbonizing route. This nanocomposite strongly interacts with Simaterial, providing a robust nanoarchitecture with abundant conductive pathways for Li-ion transport. CMC and PAA with alarge number of carboxyl groups provide binding ability by sturdy three-dimensional (3D) cross-linked network with relativelya thin SiO2 mechanical binding film on the surface of Si nanoparticles onto a highly porous carbon and forming a stablesolid electrolyte interface (SEI) layer. Meanwhile, graphenized PAN provides a highly interconnected conductivenanoarchitecture of a nitrogen-doped graphenized-like structure (NG), which provides enhanced pathways for lithium iondiffusion. Without any conductive additives, this nanocomposite material not only shows a high superior 1st dischargecapacity of 3473 mAh g-1, high initial Coulombic efficiency of 89%, excellent rate capability, and remarkable cycling life formore 600 cycles when cycled at high current density of 3000 mA g-1, but also maintaining good cyclability with a constanthigh areal capacity of ~ 2.7 mAh cm-2. Together with the ease of fabrication, this provides a promising avenue forcommercial LIBs. Figure 1

A robust network binder via localized linking by small molecules for high-areal-capacity silicon anodes in lithium-ion batteries

Silicon is known for high-capacity yet large-volume-change properties when used as lithium storage material. Polymeric binders substantially contribute to improving the cycling life and increasing areal capacity of silicon anode. Herein, a robust network binder (PG-c-ECH) via localized linking by small molecules is proposed to achieve stable cycling performance of silicon anode with high areal capacity. Peach gum (PG) is rich in abundant hydroxyl and carboxyl groups that conventionally ensure a strong binding affinity between the PG and Si. The epichlorohydrin (ECH) introduced as the short-chain chemical crosslinker further enhances the localized linking for the polymer chains. The resultant PG-c-ECH owns durable interfacial adhesion and outstanding mechanical properties to stabilize the structural integrity of Si anode. Herein, a robust network binder (PG-c-ECH) via localized linking by small molecules is proposed for high-areal-capacity Si anode. Because of its strong interfacial adhesion and excellent mechanical properties, the PG-c-ECH binder could tolerate the huge volume changes of Si active materials during repeated cycling. The Si electrodes using PG-c-ECH as the binder exhibit stable cycling performances at practical-level areal capacities. • A robust network binder (PG-c-ECH) via localized linking by small molecules is proposed. • The Si@PG-c-ECH electrode can be cycled over 10 mAh cm −2 for 35 cycles. • The Si@PG-c-ECH electrode achieves an ultrahigh discharge areal capacity of 60.00 mAh cm −2 . • The full-cell using the Si@PG-c-ECH anode shows a relatively stable cycling performance.

Voltage Hysteresis Model for Silicon Electrodes for Lithium Ion Batteries, Including Multi-Step Phase Transformations, Crystallization and Amorphization

Silicon has been an attractive alternative to graphite as an anode material in lithium ion batteries (LIBs). The development of better silicon electrodes and optimization of their operating conditions for longer cycle life require a quantitative understanding of the lithiation/delithiation mechanisms of silicon and how they are linked to the electrode behaviors. Herein we present a zero-dimensional mechanistic model of silicon anodes in LIBs. The model, for the first time, considers the multi-step phase transformations, crystallization and amorphization of different lithium-silicon phases during cycling while being able to capture the electrode behaviors under different lithiation depths. Based on the model, a linkage between the underlying reaction processes and electrochemical performance is established. In particular, the two sloping voltage plateaus at low lithiation depth are correlated with two electrochemical phase transformations and the emergence of the single broad plateau at high lithiation depth is correlated with the amorphization of c-Li15Si4. The model is then used to study the effects of crystallization rate and surface energy barriers, which clarifies the role of surface energy and particle size in determining the performance behaviors of silicon. The model is a necessary tool for future design and development of high-energy-density, longer-life silicon-based LIBs.

Highly Elastic Block Copolymer Binders for Silicon Anodes in Lithium-Ion Batteries.

Silicon (Si) is a promising anode material to replace the broadly adopted graphite due to its high capacity and abundant source. However, Si anodes suffer from severe problems of huge volume change (∼300%), and the commonly used binders like poly(vinylidene fluoride) (PVDF) cannot accommodate such changes. Here, we report a tough block copolymer PVDF-b-Teflon (PTFE) binder that can coalesce pulverized Si and thus enhance the stability of Si anodes. The suspension copolymerization of vinylidene fluoride and tetrafluoroethylene produces elastic PVDF-b-PTFE with large breaking elongations of >250% and high viscosity as well as high ionic conductivity and thermal stability. We show that 5 wt % of the binder forms elastic cobweb structures in the electrode matrix that can effectively coalesce Si particles and conductive agents together, enabling long cycling stability (>250 cycles) and high rate performance (1 C) for electrodes at a commercial-level Si loading of 1 mg·cm-2. The findings point out to a promising strategy for developing highly elastic and tenacious binders for electrodes with large volume changes during the electrochemical reactions.

Slime-inspired polyacrylic acid-borax crosslinked binder for high-capacity bulk silicon anodes in lithium-ion batteries

Binder plays a key role in maintaining the integrity of battery electrodes. In this work, we investigate the relationship between binder properties and performances of Si electrodes in a lithium-ion battery (LIB). We learn from nature and use borax as a crosslinker between strands of polyacrylic acid (PAA) to form a network in the binder. By adding different amounts of borax, we can control the degree of crosslinking and thus the mechanical and chemical properties of the binder. We find that increasing the amount of borax crosslinker increases the modulus of the polymer network and the stability of the corresponding Si electrode up to about 5 wt% borax. Even with Si microparticles with an electrode density of 1.25 g cm−3, we obtain a capacity of about 2470 mA h g−1 (3.1 mA h cm−2) and a capacity retention of 91.2% after 50 cycles. Cycle performance is extended beyond 500 cycles with a capacity limitation of 1000 mA h g−1. Though, excessive amount of borax consumes the functional groups of PAA and compromises electrode adhesion, resulting in a decrease in cycle stability. Striking a balance between mechanical strength and adhesion of the binder is important for further development of alloy-based anode materials for LIBs.

Surface SiO2 Thickness Controls Uniform-to-Localized Transition in Lithiation of Silicon Anodes for Lithium-Ion Batteries.

Silicon is a promising anode material for lithium-ion batteries because of its high capacity, but its widespread adoption has been hampered by a low cycle life arising from mechanical failure and the absence of a stable solid-electrolyte interphase (SEI). Understanding SEI formation and its impact on cycle life is made more complex by the oxidation of silicon materials in air or during synthesis, which leads to SiOx coatings of varying thicknesses that form the true surface of the electrode. In this paper, the lithiation of SiO2-coated Si is studied in a controlled manner using SiO2 coatings of different thicknesses grown on Si wafers via thermal oxidation. SiO2 thickness has a profound effect on lithiation: below 2 nm, SEI formation followed by uniform lithiation occurs at positive voltages versus Li/Li+. Si lithiation is reversible, and SiO2 lithiation is largely irreversible. Above 2 nm SiO2, voltammetric currents decrease exponentially with SiO2 thickness. For 2-3 nm SiO2, SEI formation above 0.1 V is suppressed, but a hold at low or negative voltages can initiate charge transfer whereupon SEI formation and uniform lithiation occur. Cycling of Si anodes with an SiO2 coating thinner than 3 nm occurs at high Coulombic efficiency (CE). If an SiO2 coating is thicker than 3-4 nm, the behavior is totally different: lithiation at positive voltages is strongly inhibited, and lithiation occurs at poor CE and is highly localized at pinholes which grow over time. As they grow, lithiation becomes more facile and the CE increases. Pinhole growth is proposed to occur via rapid transport of Li along the SiO2/Si interface radially outward from an existing pinhole, followed by the lithiation of SiO2 from the interface outward.

Effect of Phosphorus Doping on Conductivity, Diffusion, and High Rate Capability in Silicon Anode for Lithium-Ion Batteries

Poor long-term cycling stability and rate capability seriously restricted the commercial applications of silicon (Si) anodes, because of the huge volume change and the kinetic problems linked to th...

Improving the cyclability of silicon anodes for lithium-ion batteries using a simple pre-lithiation method

Despite intense studies into silicon anode materials, the large volume expansion of silicon remains a significant problem that reduces battery performance and shortens battery life. In this paper, a procedure to increase the cycle life of the silicon anode in full-cell configuration using a simple pre-lithiation method is proposed. By precisely controlling the thickness of the pre-deposited lithium through evaporation, the volume change of the silicon-containing anodes can be effectively reduced during discharge. A coin-cell fabricated with a high-capacity cathode and the pre-lithiated silicon–graphite anode shows improvements in cycling performance, as well as a higher discharge capacity. Electrochemical and microscopic analysis confirm that pre-lithiation successfully suppresses the volumetric changes. Thus, this work provides an effective method for the preparation of long-cycle-life Li-ion batteries containing silicon-based anodes.

Acrylic random copolymer and network binders for silicon anodes in lithium-ion batteries

The choice of a binder can greatly influence the electrochemical performance of lithium-ion batteries (LIBs), especially for silicon (Si) anodes. To systematically modulate the mechanical properties of binders and to investigate their impact on the electrochemical properties, we synthesize a series of random copolymers consisting of acrylic acid (AA) and n-butyl acrylate (n-BA) via reversible addition-fragmentation chain-transfer (RAFT) polymerization. The electrochemical properties of Si nanoparticle (SiNP) anodes prepared using copolymer binders exhibit a strong dependence on the relative composition of AA and n-BA. The incorporation of a moderate amount of n-BA (10–30 mol%) in the copolymer binder provides better cycling stability compared to a SiNP anode prepared using poly(acrylic acid) (PAA) binder. The binder containing 30 mol% of n-BA is further crosslinked by in-situ crosslinking using a variable amount of polyethylene glycol diglycidyl ether (PEGDE). The electrochemical properties (3050 mAh g−1 in the 1st cycle and 40% capacity retention in the 100th cycle at 0.5 A g−1) of a SiNP anode prepared using the crosslinked binder with 14 wt% of PEGDE show further improvement compared to those of a SiNP anode prepared using PAA binder (2310 mAh g−1 and 32% capacity retention in the 100th cycle at 0.5 A g−1).

Highly stable multi-layered silicon-intercalated graphene anodes for lithium-ion batteries

Abstract

Microporous Binder for the Silicon-Based Lithium-Ion Battery Anode with Exceptional Rate Capability and Improved Cyclic Performance.

Silicon anodes have attracted much attention owing to their high theoretical capacity. Nonetheless, an inevitable and enormous volumetric expansion of silicon in the lithiated state restrained the development of the silicon anode for lithium-ion batteries. Fortunately, the utilization of the high-performance binder is a promising and effective way to overcome such obstacles. Herein, a polymer of intrinsic microporosity (PIM) is applied as the binder for the silicon anode, which is composed of a rigid polymer backbone, an intrinsic porous structure, and active carboxyl groups (PIM-COOH). Compared to the traditional binder, both the long-term stability and rate performance of the electrode using PIM-COOH as the binder are significantly improved. The mechanism responsible for the enhanced performance is investigated. The PIM-COOH binder provides stronger adhesion toward the current collector than the conventional binders. The unique rigid polymer backbone and porous structure of the PIM-COOH binder enable a good capability to withstand the volume change and external stress generated by the Si anode. The porous structure of the PIM-COOH binder enhances lithium-ion transportation compared to the SA binder, which improves rate performance of the silicon anode. This work provides a unique insight into design, synthesis, and utilization of the binders for lithium-ion batteries.

A conductive self-healing hydrogel binder for high-performance silicon anodes in lithium-ion batteries

Although silicon has been viewed as the ideal anode material due to its superior specific capacity, silicon materials easily break down because of its large volume changes during frequent charge-discharge cycles. Polymeric binders play key roles on maintaining the mechanical integrity of electrodes and contributing substantially to improving cycle lives. Here, we design and prepare that a novel conductive self-healing hydrogel (ESVCA) binder with 3D conductive network, excellent stretchablity and fast self-healing ability coating on the surface the Si particle by in-situ polymerization method. The stretchable 3D self-healable network structure could effectively restrain the huge volume change of Si particles during lithiation and delithiation cycles to maintain mechanical integrity of the Si electrodes while 3D continuous electron transport pathways insuring the high conductivities and better electric contacts among active Si particles. The Si-ESVCA electrode not only exhibits a reversible capacity of 1786 mA h g−1 at 500 mA g−1 with a capacity retention of 71.3% after 200 cycles at ambient temperature, but also maintains superior cycling stability with a capacity retention of 74.1% and remains a high reversible capacity of 1743 mA h g−1 after 200 cycles at current density of 2000 mA g−1 at elevated temperature.